BELFAST, NOV. 8 -- A massive bomb, believed to have been planted by the Irish Republican Army (IRA), killed 11 persons and injured 53 today when it exploded in a crowd gathered for a memorial service for British war dead.

The bombing, in the Fermanagh County town of Enniskillen, about 80 miles southwest of Belfast, was the deadliest terrorist attack in Northern Ireland in nearly five years.

The bomb exploded at 10:45 a.m. inside the town's community center, where nearly 500 people -- mostly parents and their children -- had sought shelter from a driving rain. The blast, from what authorities determined was a 30-pound bomb of homemade explosives, occurred about five minutes before the start of an annual Remembrance Day ceremony at a nearby war memorial. It honors soldiers from Northern Ireland who were killed serving in the British forces during the two world wars.

Four of the dead were married couples, and 13 of the injured were children aged 2 to 15.

Those killed or injured were blown by the explosion against a sidewalk railing and then trapped under rubble when a two-story wall fell on them.

Later, in a possible retaliation by Protestant extremists, five Roman Catholic youths were shot and injured in Belfast, police said. United Press International quoted police as saying that the five were shot from a passing car in front of a hotel in the city center.

In Enniskillen, a cloud of dust filled the streets when the wall collapsed. There was a moment of shocked silence. Then soldiers and policemen, parents and children rushed to the rubble, tearing at the broken brickwork with their bare hands to find survivors.

A 14-year-old boy, who was preparing to lay a wreath at the war memorial when the bomb exploded, told The Associated Press, "I dropped the wreath and rushed to where the wall had collapsed. People were screaming, and we did all we could to pull them out.

"At 11 o'clock we should have been remembering the dead, not digging them out."

One of the young rescuers searching through the rubble found the body of his mother.

"I have seen scenes I would certainly not want to see again in my life. There were little children wondering where their parents were and parents looking for children," Archbishop Robin Eames, primate of the Church of Ireland, told United Press International. Eames was in Enniskillen to preside over the memorial service.

No one claimed responsibility for the blast, but it was believed to be the work of the outlawed IRA. Today's deaths bring to 87 this year's toll in the IRA's battle to drive the British out of Northern Ireland. The local branch of Sinn Fein, the legal political wing of the IRA, issued a statement that expressed shock at the loss of life, the AP reported.

Today's death toll is the highest in a single incident in Northern Ireland since December 1982 when 17 people were killed, including 11 off-duty soldiers, by a bomb planted by the Irish National Liberation Army -- a more extreme group than the IRA -- in a bar in Ballykelly, County Derry.

If the IRA was responsible -- and currently it is the only paramilitary organization in Northern Ireland capable of mounting such an attack -- observers believe that the attack would be an attempt to prove that it is still in business, despite a series of setbacks in recent weeks.

Thirteen IRA members have been killed this year, including two who were blown up by their own bomb two weeks ago.

Last weekend, the IRA reportedly lost 150 tons of arms and ammunition, allegedly including surface-to-air missiles, when a freighter en route to Ireland was seized off the coast of northern France. On board were three known IRA members.