Two men were being questioned Wednesday over a second deadly attack on Northern Ireland's security forces in 48 hours, prompting warnings the province faces a return to violence.
British and Irish ministers, meanwhile, held an emergency meeting in the troubled province Tuesday evening, vowing that dissidents would "not have the power to stop the peace process."
The killing of a policeman on Monday followed deaths of two British soldiers on the weekend, stoking fears that Northern Ireland could be plunged back into the sectarian bloodshed which wracked the province for 30 years.
|Police guard a grey skoda vehicle (Background R) in which a policeman was killed in Craigavon, Northern Ireland.|
Policeman Stephen Carroll, 48, was shot in the head in a republican area in Craigavon, 20 miles (30 kilometres) southwest of Belfast, police said, and the Continuity IRA (Irish Republican Army) claimed responsibility for the killing.
After a day of investigations Tuesday, police announced late in the day that they had arrested two men, aged 37 and 17, in Craigavon in connection with Carroll's murder.
"They may have the power to take the life of a policeman or two unarmed soldiers but they do not have the power to stop the peace process," Britain's Northern Ireland Minister Shaun Woodward said, following a meeting with his Irish counterpart and other ministers at Hillsborough Castle in County Down.
"The people of Ireland did not want it to happen and would not follow a bunch of fanatical criminals."
The policeman's murder came after two soldiers were killed late Saturday at the Massereene barracks in Antrim, northwest of Belfast, in an attack claimed by another dissident republican group, the Real IRA.
The soldiers were the first killed in Northern Ireland for 12 years, while Carroll was the first policeman murdered in the province since 1998.
Reacting to the Craigavon shooting, British Prime Minister Gordon Brown vowed that Northern Ireland would not see a return of the so-called Troubles, which killed over 3,500 people until the landmark 1998 Good Friday agreement.
"There will be no return to the old days," he said.
The province's political leaders vowed that the violence would not prevent Protestants and Catholics from sharing power, as they have done since 2007.
Northern Ireland's First Minister Peter Robinson said he was "sickened", while his deputy Martin McGuinness issued a strongly-worded condemnation, after his republican Sinn Fein party was criticised for being slow to condemn the first attack.
"These people are traitors to the island of Ireland, they have betrayed the political desires, hopes and aspirations of all of the people who live on this island," he said. "They don't deserve to be supported by anyone."
The two Northern Ireland leaders postponed a planned investment-seeking trip to the United States after the attacks, and notably spent 20 minutes with the wife of the dead policeman.
But a spokesman said they were planning to head to the United States Wednesday, for a visit which will include talks with President Barack Obama in the White House on Saint Patrick's Day next week.
Irish Prime Minister Brian Cowen added: "The people and all of their democratic representatives reject this violence and will overcome the evil and unrepresentative minority who want to drag us back to the past."
Cowen, who is also due to meet with Obama on Saint Patrick's Day, told lawmakers an agreed all-party motion would make clear the Dail's (lower house of parliament) condemnation at the attacks by individuals who claimed to act on behalf of the Irish people.
Dolores Kelly, a nationalist SDLP lawmaker in Belfast and member of the Northern Ireland policing board, added: "We are staring into the abyss and I would appeal to people to pull back."
The Continuity IRA and the Real IRA are both splinter groups of the IRA, which has laid down its arms and was the military wing of Catholic socialists Sinn Fein, which now shares power in Northern Ireland with conservative Protestant former foes the Democratic Unionists.
The Real IRA was behind Northern Ireland's most deadly attack, the 1998 Omagh bombing which killed 29 people.