The murders of two soldiers in Northern Ireland will not derail the peace process, Gordon Brown insisted today.
The Prime Minister sent his condolences after gunmen opened fire outside Massereene Barracks in Antrim last night.
Mr Brown said: "I can assure you that we will bring these people to justice."
Mr Brown branded the attack "cowardly", adding: "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."
The victims were understood to be taking delivery of a pizza when the attackers pulled up in a vehicle and opened fire. Four other people were seriously injured.
No-one has yet claimed responsibility for the shooting, but dissident republicans opposed to the peace process were immediately blamed.
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.
Police are understood to be examining a car found abandoned in the nearby town of Randalstown. Officers are trying to establish whether the vehicle was used in the shooting.
The incident happened 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.
The gunmen's car or van pulled up outside the barracks' main gates shortly before 10pm while soldiers and security staff were taking delivery, it is understood. Police said the pizza delivery staff were not involved in the attack.
Secretary of State for Northern Ireland Shaun Woodward condemned the shooting as an "act of criminal barbarism".
He said: "My thoughts are with the families of those killed and injured in this murderous attack. The Prime Minister is being kept closely informed.
"The contrast between those who serve the community and those who would destroy it could not be clearer.
"The people who did this will be pursued and they can be assured that they will never be able stop political progress in Northern Ireland."
Downing Street added: "This is a terrible incident that we utterly condemn and the Prime Minister's thoughts, first and foremost, are with the families of those killed and with those seriously injured in this attack.
"In recent days action has been taken to increase security in Northern Ireland. This is because of the increased threat from those who, even at this late stage, wish to ignore the wishes of the overwhelming majority of the people of Northern Ireland and attempt to derail the peace process.
"The full facts of this incident are being investigated. We will do everything we can to ensure those responsible are brought to justice."
Witnesses reported hearing two long busts of gunfire as a car drove by the barracks - home to 38 Engineer Regiment.
At least six ambulances and three paramedic vehicles rushed to the scene as emergency sirens blared from inside the complex.
The injured were taken to Antrim Area Hospital, about a mile away.
The area around the barracks has been sealed off with a massive security operation under way.
A statement from the Ministry of Defence said: "It is with deep regret that we confirm the deaths of two soldiers and injuries to four other persons in an attack at Massereene Barracks in Antrim, Northern Ireland.
"The next of kin are being informed and further information will be released in due course. The circumstances and details of the attack are currently under investigation by the Police Service of Northern Ireland (PSNI)."
Northern Ireland's First Minister and Democratic Unionist Party leader Peter Robinson said he was postponing a trip to the United States as a result of the shootings.
He said they were a "terrible reminder of the events of the past".
Mr Robinson added: "These murders were a futile act by those who command no public support and have no prospect of success in their campaign. It will not succeed."
Ian Paisley Jr, a member of the Policing Board, said last night: "This could be a defining moment in the history of Northern Ireland."
The Democratic Unionist member of the Northern Ireland Assembly added: "For the last 10 years, people believed things like this happened in foreign countries, places like Basra. Unfortunately it has returned to our doorstep.
"There are people who have been intent on murdering police officers or soldiers, or someone else, to strike home and galvanise support for some mad cause. This is where we are tonight.
"Some people also tried to exaggerate that message, and if this shooting is attributed to dissident republicans, then it was no exaggeration.
"The police have managed to keep the lid on this and they have had some successes against these people which they've kept quiet. They have disrupted and harried them, but its the people of Northern Ireland who will suffer."
Security chiefs had warned for months that dissident republicans were determined to inflict fatalities. Five police officers, two of them off-duty, were wounded in separate gun and bomb attacks in Londonderry, Dungannon, Co Tyrone, near Castlederg, also Tyrone, and not far from Roslea, Co Fermanagh, where the threat has been at its highest.
There have also been a series of failed bomb attacks, one just a few weeks ago near Castlewellan, Co Down.
The last soldier to be murdered in Northern Ireland was Lance Bombardier Stephen Restorick, 23, who was shot by an IRA sniper at a checkpoint in Bessbrook, County Armagh in February 1997.
The 38 Engineer Regiment has been based at Massereene Barracks since August last year but is due to be relocated to RAF Aldergrove in Co Antrim by the end of 2010.
Kylie McLaughlin, who lives near the barracks, heard the attack. She told the BBC: "It was constant fire like a machine gun.
"It was very scary, we were not sure what was happening. We just can't believe it has happened here."
The SDLP's Thomas Burns MLA said: "We condemn this attack.
"This has taken us back to the bad, bad old days which we have left long since behind.
"It will cause the power sharing executive to wobble a bit - we are all very, very concerned about that."
He added: "We are interested about moving Northern Ireland forward.
"We want to see a prosperous Northern Ireland, we don't want to see people getting shot in the street."
It emerged last week that intelligence service MI5 was still allocating 15% of its resources in 2007-2008 to anti-terrorism activities in Northern Ireland.
The Intelligence & Security Committee Report also said that dissident republicans continued to pose a threat in Northern Ireland and the rest of the UK.