IRA CLAIMS RESPONSIBILITY FOR BLAST.

Byline: Sarah Lyall The New York Times

The Irish Republican Army claimed responsibility Monday for the bomb that tore through a double-decker bus in central London late Sunday night, and police said there was a chance the single body they pulled from the wreckage was that of the bomber. Nine others were injured in the explosion.

The bombing was the third in 10 days in an increasingly frightened London and left few doubts that the IRA was resuming a full-scale campaign of violence on the mainland. London is already on a high security alert, and the IRA said it might well expand its bombings to other major English cities, Irish National Radio reported Monday.

Because the police received no warning of Sunday's explosion, they said they were inclined to conclude that the bomb had exploded prematurely while it was being carried by a passenger on the bus.

"The bus was not the intended target, we believe," said Cmdr. John Grieve of Scotland Yard's anti-terrorist branch.

The IRA provided advance warning before setting off each of the first two bombs - one that exploded in a parking lot in the Docklands area of east London on Feb. 9, and another, in the West End, that was discovered Thursday and destroyed before it could go off. But with Sunday's bomb, which went off near the hotels and theaters in tourist-heavy central London, not far from Covent Garden, the explanation came afterward.

"The bomb which exploded last night was one of our devices," the group said Monday in a terse statement to the British Broadcasting Corporation in Belfast. "We can say at this stage that we regret the loss of life and injuries which occurred."

The bomb, which exploded at 10:38 p.m., blew windows out of nearby buildings and blasted shards of glass and twisted steel through the area. For most of Monday, a wide swath remained closed to cars and pedestrians as police continued examining the wreckage.

In declaring an end to its 17-month cease-fire 10 days ago, the IRA said it no longer could countenance the slow progress of talks over the future of Northern Ireland. The crux of the dispute is whether the province, which has a Protestant majority, should remain part of Britain, join the mostly-Catholic Republic of Ireland, or assume some other status.

But Sunday's bomb seemed to go wrong. It was not the first time an IRA bomb blew up before it was intended to, killing or severely injuring the people transporting it. The police in Northern Ireland call such bombs "OGs," or "own goals," after the practice of mistakenly scoring against your own team in soccer.

In the most famous example, a bomb carried by two IRA agents and meant for Protestant leaders in Belfast two years ago exploded prematurely, killing one of the bombers as well as nine people in and near a fish shop.

In another incident, a young couple posing as sweethearts were killed as a bomb intended for an army band blew up as they placed it in a doorway in St. Albans, a suburb of London.

Grieve would not say whether the body found in the ruined bus Monday morning was that of the bomber. "That's not a possibility we have discounted yet," he said. "There is a considerable amount of scientific work to be done at the scene."

Another theory was that the bomber might have been one of the three seriously injured people.