The officer, named locally as Paul Musgrave, had just left work when he was shot a number of times in an arm as he sat in his car at traffic lights at 5.30pm yesterday.

He managed to drive back to Dungannon Police Station and was taken to Craigavon Area Hospital where he is in a stable condition.

A man and a woman were arrested today in connection with the attack, which is the second shooting of a police officer in five days.

The Real IRA shot 43-year-old Jim Doherty, a Catholic police officer, in Londonderry last Thursday as he dropped his child off at school.

Mr Doherty suffered injuries to his face and arm and is still being treated in hospital.

Sir Orde said the shootings were "extremely sinister".

"This has taken cowardice to new levels. The important point is this will not deter police officers going about their day to day duty. We will carry on despite of the threat. If they wish to continue this we will pursue them to the end of the earth," he told the BBC.

Secretary of State Shaun Woodward described yesterday's attack as " despicable and cowardly", while Sinn Fein's Martin McGuinness said those responsible had no popular support and urged anyone with information to contact police.

The Deputy First Minister said: "These people have no popular support and no strategy to achieve a united Ireland.

"These people are attempting to plunge our society back into conflict. I am confident the vast majority of people here will ensure that this does not happen."

DUP South Antrim MP William McCrea said there was an orchestrated intimidation campaign against police officers in Northern Ireland and called on the PSNI to "crush these dissident groups".

"There must be no let-up in the campaign against dissident republicans," he said.

Mr McCrea added: "All parties across Northern Ireland and the Government must pledge their support to the police in the fight against these groups.

"They must be shut down and put out of business once and for all. I intend to raise this matter at Westminster and will be urging the Government to act accordingly.

"We won't allow a blind eye to be turned to these acts."

The DUP's Lord Morrow said he believed the attack was timed to coincide with Sinn Fein nominating DPP members at Dungannon Council last night.

"I am absolutely horrified and I am absolutely sickened," he said.

"It is time the Government got the gloves off and allowed the PSNI to crush this dissident faction of republicans that are intent on causing maximum damage."

It is understood that police officers in certain areas have been briefed about threats against them from dissident republicans, with some officers having to move house because of the threat.