Two pizza delivery men are among those seriously injured in the attack on an army barracks in Northern Ireland that left two soldiers dead, police said today.

Investigating officer Detective Superintendent Derek Williamson said at least two gunmen opened fire indiscriminately on a group of soldiers and the two delivery men as they arrived at Massereene Barracks in Antrim last night.

He said the gunmen fired one burst with automatic weapons then walked forward and shot the victims as they lay on the ground. The two soldiers who were killed were both aged in their early twenties and were due to fly to Afghanistan on active service in the coming days.

As well as the pizza delivery men, who police also said were very young, two other people were injured in the attack, which has been blamed on dissident republicans opposed to the peace process.

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One of the injured is critical, two are serious and one is serious, but stable.

Appealing for witnesses, Chief Superintendent Williamson said: "I have no doubt in my mind this was an attempt at mass murder."

The investigating officer said police were investigating whether the gunmen had deliberately targeted the pizza men as well as the soldiers.

He said Dominos Pizza in the town had received two separate delivery orders from the base at around 9.20pm. The orders were sent out separately and the two delivery men arrived one after the other.

It was at this point when gunmen opened fire from a car.

"Last night two very young men lost their lives in a very callous and a very ruthless attack by terrorists who have no thought and had no thought last night for anyone who was in the vicinity.

"Indeed the attack took place at a time when two other young men, two civilians, who were delivering pizzas to the Massereene Barracks stopped, and it is clear from what we know at this stage that the terrorists not only wanted to kill soldiers who were there last night, but also to try to kill those two pizza delivery men."

He added: "The gunmen, having fired an initial volley of shots, moved forward when people were on the ground and fired additional shots at those people on the ground, so it was a very, very callous and very ruthless attack."

Gordon Brown

Gordon Brown today insisted the murderers would not derail the peace process.

The Prime Minister sent his condolences, saying: "I can assure you that we will bring these people to justice."

Branding the attack "cowardly", he added: "Our first priority has always been the safety of people in Northern Ireland, and we will do everything in our power to make sure that Northern Ireland is safe and secure."

He went on: "No murderer will be able to derail the peace process, that has the support of the vast majority of the people of Northern Ireland.

"We will step up our efforts to make the peace process one that lasts and endures."

Outrage

The attack prompted expressions of outrage and dismay from those in the UK and Ireland.

Defence Secretary John Hutton said: "I wish to express my sincere condolences to the families, friends and comrades of the two soldiers who were tragically murdered last night and those who were injured. My thoughts are with them all at this extremely difficult time.

"This senseless attack has only served to cause grief and dismay throughout Northern Ireland. No cause or grievance can justify such a cold blooded act."

Business Secretary Lord Mandelson, a former Northern Ireland Secretary, said the shootings were not "the return of something that is going to destabilise or throw away the peace process".

"I would like to offer my condolences to the families of those killed or injured in what is just plain cowardly, futile and barbarism," he told BBC1's Andrew Marr show.

"But the difference between Northern Ireland now and in the past is that all shades of political opinion is going to be united in condemning what was done last night.

"There is nobody in Northern Ireland who wants to take the province back to its violent past."

Mary McAleese

Irish president Mary McAleese today expressed her shock and dismay.

"The president condemned the violence in the strongest terms and said that her thoughts and prayers were with the families of the those who had been killed and with the injured," said a spokeswoman.

Liberal Democrat home affairs spokesman Chris Huhne described the attack as an "outrage" which he blamed on a "very small dissident minority".

He told Sky News' Sunday Live: "It's obviously a very regrettable, appalling event that we have begun to see any violence in Northern Ireland after all the successes of the peace process."

The attack came just 36 hours after Northern Ireland Chief Constable Sir Hugh Orde confirmed that undercover soldiers had been called in to carry out surveillance operations on dissidents amid warnings that the threat against his officers and military personnel was at its highest for almost a decade.

Mr Huhne said the Police Service of Northern Ireland (PSNI) had "got a grip" on what was going on but "unfortunately not enough to stop them".

Mr Huhne continued: "The vast bulk of the republican movement is committed to the peace process and wants to see peaceful progress in Northern Ireland.

"The people who are responsible for this outrage in Northern Ireland against British soldiers are a very small dissident minority of the republican movement and I think they will cause as much shock and revulsion amongst many republicans as they will amongst everyone else."

Shaun Woodward

Northern Ireland Secretary of State Shaun Woodward said it was clear the shooting was not just an opportunist attack.

"This was a pre-planned attack at mass murder not only on off-duty soldiers but on civilians."

He rejected any notion that security around the base had been lax when the gunmen struck.

Mr Woodward said the incident while tragic, did not represent a return to Northern Ireland's dark past and insisted the peace process would go on and would succeed despite the efforts of the dissidents to destabilise it.

"Northern Ireland is now a different place," he said.

"Regrettably, a handful of people remain in the grip of a violent past but we will find them and prevent them doing this in the future."

The Secretary of State revealed that the soldiers killed would have been engaged in humanitarian work during their planned deployment to Afghanistan.

"These soldiers were actually about to be deployed to Afghanistan. They were off duty. These are soldiers who are doing humanitarian work around the world, these are soldiers who are part of our great tradition of public service and the cowardly inhumane attack that took place last night must be utterly condemned."

Mr Woodward also paid tribute to the response of the soldiers' colleagues in the wake of the shooting.

"I want to pay tribute to the men and women here at 38 (Engineering Regiment).

"They are remarkable people, they did a remarkable job last night in the face of the most cowardly, despicable criminal behaviour by those who perpetrated the attack at this base."

Shadow foreign secretary William Hague said the attack was evidence that some people in Northern Ireland wanted it to "go back into its old sectarian ways".

He told Sky News' Sunday Live programme: "It is astonishing there are people stupid enough, crazy enough to want that to happen.

"It means that everybody else, and that is the, I think, 99% of the people of Northern Ireland, must make sure that doesn't happen."

Commenting on Sir Hugh's warnings, Mr Hague said: "It shows that we should take very seriously the times when people of his seniority and position say these things."

"There has been a pattern emerging of some time of an increased risk of terrorist attack or murder and so we should take that seriously, this is sad evidence of that.

"The lesson for all of us is that we must reinforce the peace process, make sure that these things can achieve nothing.

"That is the important lesson to the perpetrators of these crimes - there is nothing that they can achieve by doing these things.

"They have no popular support in Northern Ireland or anywhere else and they are not going to achieve anything at all."

Jacqui Smith

Home Secretary Jacqui Smith described the shooting as a "vicious and barbaric attack".

She told Sky News' Sunday Live: "Things like this won't be able to derail a process which has the support of the vast majority of people in Northern Ireland."

Asked about Sir Hugh's concerns, Ms Smith said: "We will make sure that wherever there are people who want to kill or maim in whatever name we will have the resources in place in order to prevent that from happening."

She added: "In Northern Ireland real progress has been made through a political process that local politicians have been willing to work incredibly hard on and which the vast majority of people in Northern Ireland support.

"I think it is that which is going to be the real opposition to the sort of brutal killing of both civilians and armed forces that we have seen today."

Irish Government

The Irish Government pledged the full support of the Garda in investigating the attack.

Garda Commissioner Fachtna Murphy held talks this morning with Sir Hugh Orde and offered full co-operation in the fight against dissident paramilitary activity.

"The high level of co-operation that already exists between the two forces will be maintained and no effort will be spared on our part," Irish Justice Minister Dermot Ahern said.

"I join with my colleagues in unreservedly condemning this attack and the senseless loss of life.

"I want to offer my condolences to the families of those who have lost their lives and to those who have been injured."

The Garda Commissioner, Sir Hugh and senior British and Irish government officials are due to meet to discuss security issues in coming days.

Peter Robinson: No retaliation

Northern Ireland's First Minister and DUP leader Peter Robinson said there must not be any retaliation for the attack .

"Can I urge all of those who may be angry within the Unionist community. This is a matter to be left entirely with the police and the authorities to deal with. They are capable of dealing with it and they shall deal with it and we must give them our full support."

Local MP for the area, William McCrea, revealed that one of the pizza delivery men was a foreign national.

He added: "Not only were two young men in their early 20s brutally murdered, but also there was a determined and deliberate attack upon the young pizza deliverers as well.

"In fact the gunmen deliberately fired at them to kill them as well. There's nothing but murder in the hearts of theses people, but one thing I can guarantee they will not defeat us, they will not win, but we will see them defeated."

Suspect vehicle

Police have confirmed that they are examining a suspect vehicle abandoned in the nearby town of Randalstown.

The car was left at around 11pm last night and police are investigating whether it was the vehicle used by the gunmen.

Mr Robinson added that he was confident the terrorists would not succeed in their objective of destabilising the peace process.

"I believe that all that they will achieve is to galvanise every right thinking person in this community who will together say we are not going back and I believe that will be the view of people irrespective of their political party or their religious affiliation."

Irish opposition leaders said the vicious attack had chilling echoes of dark times people hoped would never return.

"We have grown accustomed to a peace that has allowed all communities on the island to look to the future with optimism," said Fine Gael leader Enda Kenny.

"This brutal assault last night is a throwback to a period that we all hoped was in our past."

He added: "There is no place in our society today for vicious attacks of this nature and I expect those responsible to be brought to justice."

Labour Party leader Eamon Gilmore said the killings are particularly deplorable at a time when of power-sharing and comprehensive policing reform in Northern Ireland.

"I hope that the PSNI will get full cooperation from the public in their efforts to bring those responsible to justice.

"Democrats, north and south, must work together to put all paramilitary organisations out of business."

Liberal Democrat leader Nick Clegg said hearts went out to the family and friends of the soldiers "murdered so brutally" and wished the injured a speedy recovery.

Speaking to his party's spring conference in Harrogate this afternoon, he said: "This attack is a reminder of Northern Ireland's darkest days, which have no place in its present and future."

Orde

Chief Constable Sir Hugh Orde said the deaths were a very sad day for Northern Ireland, the shootings had been carried out by cowards and a major police investigation was under way.

He said: "We have all the resources we need to do it and find the people responsible for this, who not only deliberately and determinedly drove an attack home on the British military establishment, but who were also equally determined to try and kill ordinary members of the community at the same time. People should reflect on that."

He added: "A tiny number of people are determined to drag us back to where nobody wants to be."

Sinn Fein

Sinn Fein leader Gerry Adams said the shootings were wrong and were an attack on the Northern Ireland peace process.

The MP said the perpetrators had no support and he urged party members to help the police investigation.

"Last night's attack was an attack on the peace process. It was wrong and counter productive," he said.

"Those responsible have no support, no strategy to achieve a united Ireland. Their intention is to bring British soldiers back onto the streets.

"They want to destroy the progress of recent times and to plunge Ireland back into conflict."

Mr Adams stated that Irish republicans and democrats had a duty to oppose violence and to defend the peace process.

"There should be an end to actions like the one in Antrim last night. The popular will is for peaceful and democratic change.

"Sinn Fein has a responsibility to be consistent. The logic of this is that we support the police in the apprehension of those involved in last night's attack."

Mr Adams appealed to republicans for calm, thoughtful and decisive leadership.

"The peace process was built against the odds and not least because of the willingness of republicans to take risks and to be strategic and long-sighted."

The MP claimed there are elements within Unionism and within the British government 'who do not want the peace process to achieve its objectives'.

"Our responsibility is to defend the peace process and the progress that has been made to achieving national and democratic rights.

"We will not be deflected from our republican and democratic objectives," he added.

Prayer service

At midday hundreds of churchgoers from churches across Antrim gathered at the police cordon near the murder scene to hold a prayer service.

Traffic was halted as congregations from the Roman Catholic, Church of Ireland, Presbyterian and Methodist churches came together to pray for the victims of the attack.

During the prayer service, Catholic priest Father Tony Devlin said the community was united in shock and sorrow.

"We don't want to go back to this," he said. "Nobody wants to go back to this in any way at all. None of us want it in any way at all and we pray that those who engage in this will just stop it. Go away from it, we don't want those years of the past, they were horrible years for everyone. In our churches today many people were crying because of the experiences they remembered from the past. They do not want it to come back again."

Attending the service was the regimental chaplain from Massereene barracks, Reverend Philip McCormack.

He said the troops were bearing the loss of their comrades in a professional way. "It's a very close-knit unit," he said. "People care a tremendous amount, they spent weeks and months training and preparing (for Afghanistan) and so anything like this will obviously have a profound impact. But they are very professional and we still have a job to do and we will mourn and deal with this and then we will do our job."

Scottish Secretary Jim Murphy told the Scottish Labour conference in Dundee: "We have had tragedy again over the weekend in Northern Ireland.

"I think this conference and the Labour party has again to recommit itself to the peace process and implacable opposition to any cowardly attacks of terrorism in Northern Ireland."

Mr Woodward acknowledged there was a danger that the killings could lead to an increase in sectarian tensions.

He told BBC Radio 4's The World This Weekend: "Of course there's a risk that it could revive some of those tensions.

"But I think it's very important that our response to this is proportionate too because who could have imagined that 10 years ago we would have had the leaders of all the parties across Northern Ireland together, separately, coming out condemning the act, condemning the violence, demanding that everybody comes forward with information and yet that's what we now have.

"This is a different Northern Ireland. What the real singularity of this is is that the political leaders who have come out condemning the murders today, they genuinely represent the community of Northern Ireland.

"The murderers of last night, they represent nobody."

A Downing Street spokesman said later: "The Prime Minister has spoken this morning to Brigadier Norton, the Commanding Officer of Massereene barracks, and Sir Hugh Orde to express his admiration and gratitude for the courage and dedication of the men and women under their command.

"He has also spoken to Brian Cowen and the First and Deputy First Ministers of the Northern Ireland Executive, and is being briefed regularly by the Northern Ireland Secretary and security officials.

"All are agreed that this outrageous attack will do nothing to put the peace process, which reflects the will of the overwhelming majority of the people of Northern Ireland, at risk."

Nuala O'Loan

Former Northern Ireland Police Ombudsman Nuala O'Loan issued a direct appeal to the killers to end the violence.

"Clearly there are still people who are determined to fight and determined to kill.

"To those people I would say: 'Stop. Stop because we don't need any more deaths, we don't want any more deaths. It is totally wrong. We need to move forward and protect the fragile peace we have."'

Ms O'Loan, who served as Police Ombudsman from 1999-2007, added: "There were times when we woke up day upon day to these reports on the radio of murder and mayhem. Those days are done and they must stay done.

"We must ensure this is an isolated incident and that these murderers are brought to justice.

"It is shocking, it is tragic. It is a reminder of everything we have been through for the past 40 years," she told Newstalk Radio in Dublin.

She added: "If anybody has any information, don't decide yourself if it is of any use, just give it to the police and give it fast."

Loyalist appeal

Loyalist political representatives made a plea to people within their communities not to retaliate.

Frankie Gallagher, from the Ulster Political Research Group, which has links with the paramilitary UDA, said: "The people who carried out this attack have no mandate for their futile actions and their communities, particular the Irish nationalist and republican communities in Northern Ireland must let them know that lour and clear.

"This is clearly an attack on what all communities have achieved so far and an attempt to destroy the peace process itself.

"This cowardly attack has created considerable anger in unionist communities but there must be no retaliatory actions. This situation must be dealt with entirely by the police.

"That includes politicians and civic leaders giving clear and unequivocal support to the PSNI in bringing these criminals to justice instead of scoring narrow party political points."