LONDON -- An Irish Republican Army bomb exploded in the heart of London yesterday, 300 yards from the residence of Prime Minister John Major and just 11 months after an IRA mortar attack on 10 Downing St. itself.
The bomb was secreted in a leather briefcase left between two cars parked outside a building owned by the Defense Ministry. A warning sent to two television networks gave the police time to steer morning rush-hour pedestrians and traffic away from the area of Whitehall, where the bomb had been planted and where many government offices are located.
It exploded shortly after nine a.m. There were no injuries.
The mortar attack on Feb. 12, 1991, occurred while Prime Minister Major was holding a Cabinet meeting. Yesterday, he had left No. 10 shortly before the blast.
In a statement from Dublin, the IRA claimed responsibility. The bomb was an extension of IRA campaigns of civic disruption and property destruction being waged here and in Northern Ireland. Bombs have devastated parts of central Belfast the past few weeks.
Strict security measures continued in Belfast yesterday. Traffic congestion worsened as reinforcements, called up from the Ulster Defense Regiment the past few days, carried out security checks on virtually all vehicles entering the city in an attempt to curb the bombers.
But as the army concentrated on Belfast, five IRA firebombs went off yesterday in various locations in County Antrim. The night before, a police station was bombed in Londonderry.
Nigel Dodds, the lord mayor of Belfast, and other Unionist political leaders, continued to demand more troops for Northern Ireland. Nationalist politicians, who generally speak for the Catholic minority, suggested other strategies.
"All these new security measures by British forces -- none of those are going to work," said a spokesman for Sinn Fein, the party most knowledgeable about IRA activities. "The problem needs a political answer, not a military answer."
Although the Whitehall bomb was said to contain only a few ounces of explosive -- the whole device weighed 5 pounds, police said -- a witness to the blast said, "One of the vehicles was torn to shreds. The frame was still there, but it was burnt and both doors were hanging wide open."
A policeman 80 yards from the blast was knocked off his feet. Windows along Whitehall were blown out for 100 yards.
George Churchill-Coleman, commander of the government's Anti-Terrorist Squad, said, "This kind of thing is going to happen from time to time. . . . But I must emphasize we should not overreact. To cause panic and terror is what the terrorists want."
The blast was the latest in a long series of IRA blasts, large and small, set off in and around London the past six months. They grew more frequent through the holidays, with 25 firebombs going off in December. They are designed to disrupt the working of this city of 6.3 million, and occasionally have succeeded.