A 1,000-pound bomb detonated by terrorists hiding near a rural road in this border city exploded Tuesday, killing a Roman Catholic nun and three police officers, authorities said.
An anonymous caller claimed responsibility for the attack on behalf of the Irish Republican Army in a telephone call late Tuesday to a news organization in Belfast.
The caller said the IRA had killed the four people in a "military action" and expressed no regret over the nun's death.
The slaying of a nun would be widely seen as a major embarrassment for the mainly Catholic IRA, which in recent months has escalated its terror campaign aimed at driving the British out of Northern Ireland.
It was believed to be the first time a Catholic nun has been killed in 21 years of sectarian violence in British-run Northern Ireland.
The terrorist attack--one of the deadliest in Northern Ireland this year--aroused outrage among political and religious leaders on both sides of the Irish border.
"I know all the people of Ireland join me in my condemnation of this atrocity," Prime Minister Charles Haughey of the Irish Republic said in Dublin.
The bomb, placed in a culvert under the road, was detonated as an unmarked police car passed a hayfield two miles outside Armagh, police said. The nun and a female social worker were approaching in a small car, police said.
The blast hurled the police car into the air. It smashed into a hedge and landed on its roof, apparently killing the three policemen instantly.
"The ground shook beneath us, and it was accompanied by a very large explosion," said Paul Corr, the owner of a nearby gas station.
The nun, Sister Catherine Dunne, died later in a hospital. Her companion, whose name was not released, was listed in satisfactory condition, police said. No ages were available for the two women.
Police identified the Royal Ulster Constabulary officers who died in the attack as William Hanson, 37; David Sterritt, 34, and Joshua Willis, 35.
In Belfast, a police spokesman said an unknown number of gunmen took over a house about 400 yards from the road early Tuesday and held a married couple and their children at gunpoint until shortly before the 2 p.m. bombing.
Police said a detonating wire ran from the bomb through a freshly cut hayfield to a spot near the house.