LONDON — A group calling itself "The Secret Organization of al-Qaida in Europe" claimed responsibility for yesterday's bomb attacks in London, the city's worst since World War II, saying the blasts were in retaliation for British activities in Iraq and Afghanistan.

The same organization posted new threats against Italy and Denmark, two U.S. allies with troops in Iraq, causing security officials in the United States, across Europe and as far away as Mexico to announce heightened states of alert.

The bombs ripped through three Underground trains and a red double-decker bus in central London during morning rush hour, killing at least 38 people and wounding more than 700. There were differing accounts of how many were killed.

Smoke wafted up from the entrances to the Edgware Road underground station and victims poured out, faces covered in soot, their hands pressed against bleeding heads. Some survivors ran out frantically, clutching each other, seeking safety.

In Tavistock Square, where the bus exploded, sirens wailed, ambulances raced in and emergency workers quickly swathed the victims, many shivering from shock, in silver blankets.

The explosion tore the top off the bus and rained blood and bodies on the pavement below. "One moment there was a bus there, and the next moment it peeled up like a top of sardines," said Billy Palmer, 42, a musician who witnessed the explosion from the sidewalk. "About four or five people literally came flying out the top."

Police disclosed few details about the attacks, saying only that conventional explosives were used.

London calling


For information about American citizens who may have been affected by Thursday's bombings in London, call 888-407-4747 (toll-free in the U.S.) or 202-501-4444 (regular toll line from outside the U.S. and Canada).

A senior U.S. intelligence official confirmed that British authorities had recovered evidence that timing devices were used to detonate the explosives on the subway rail cars.

He offered no further information on the devices, and said he did not know whether cellphones were used, as they were in the Madrid train bombs that killed 191 people in March 2004. The official spoke on condition of anonymity.

The official said he could not confirm reports that the attack on the double-decker bus in London was carried out by a suicide bomber. He said al-Qaida's role in the attacks, if any, had not been determined, but noted that the bombings had many of the "hallmarks" of an operation by al-Qaida or its affiliates.

"You can't draw conclusions from that, but it helps shape your thinking," the official said.

British Foreign Minister Jack Straw said the bombings bore "the hallmarks of an al-Qaida-related attack," but police said they could not confirm the claim of responsibility.

Summit disrupted

The blasts apparently were timed to coincide with the first full working day of a summit in Scotland where British Prime Minister Tony Blair was hosting leaders of the world's most industrialized nations.

While police stopped short of identifying any individuals or groups, Blair said he suspected people who claim to act "in the name of Islam."

"We will not allow violence to change our societies or our values, nor will we allow it to stop the work of this summit," Blair said, with President Bush, French President Jacques Chirac and other leaders of the Group of Eight nations at his side.

Blair returned to London and immediately went into a national-security meeting with senior advisers and Cabinet members. He went back to the summit later.

"We Spaniards know well the suffering that the British people are going through today," Prime Minister Jose Luis Rodriguez Zapatero said. "We unite with their grief as they and so many other people united with ours."

The three Underground blasts in London occurred within 26 minutes of each other, beginning at 8:51 a.m. near Liverpool Street station in the city's financial district and historic heart. London Underground officials initially thought there was a malfunction or an accident on the line.

As reports of the other explosions poured in, however, officials realized that the world's oldest subway was under lethal assault.

At 8:56 a.m., another blast occurred on the Underground between Kings Cross Station and Russell Square. It was followed at 9:17 a.m. by an explosion on a train entering Edgware Road station, which blew a hole in the side of another oncoming train.

Seven people were confirmed dead in the first explosion, 21 in the second and seven in the third. At least three people were killed in the bus explosion, which took place at the intersection of Upper Woburn Street and Tavistock Place. Officials said they recovered all the bodies from the blast scenes.

Authorities said the death toll could climb, because the wounded included 45 people who were in serious or critical condition.

Determined response

Londoners generally responded with determination, not panic. Police, firefighters, ambulance services and the Underground authority implemented long-rehearsed plans to respond to terrorist attacks. The British people had been warned repeatedly that they might face such an event since the Sept. 11, 2001, attacks in the United States. Since the Madrid train bombings, the city has been on alert for an attack against "soft" targets.

"I'm shocked like everyone else, but everyone knew something like this might happen one day," said Cristina Perez, who was evacuated from the subway after the attacks.

British authorities have tightened border controls and maintained security vigilance.

Tim O'Toole, an American who is managing director of London Underground, pledged that the entire system would be searched overnight, with the goal of restoring service today. "We are going to look at every inch of every train. ... We will do everything to keep our passengers safe," he said.

Some buses had returned to service by last night, as had the main surface rail lines.

British officials promised the most intensive terror investigation in the country's history. They were expected to scrutinize the thousands of security cameras that track people in the capital for clues to the identities of the attackers.

Maintaining policies

Blair gave no sign that he would alter his government's policies in response to the attack.

In London, Blair expressed "profound condolences to the families of the victims and for those who are casualties of this terrorist act. ... There will, of course, now be the most intense police and security-service action to make sure that we bring those responsible to justice.

"We know that these people act in the name of Islam," Blair said, "but we also know that the vast majority of Muslims here and abroad are decent and law-abiding people who abhor this act of terrorism every bit as much as we do."

The attackers, he said "are trying to use the slaughter of innocent people to cow us, to frighten us out of doing the things that we want to do, or to try to stop us going about our business as normal, as we are entitled to do, and they should not and will not succeed."

"The war on terror goes on," Bush said at Gleneagles, the Scottish golf resort where he and other Group of Eight leaders are holding their annual summit.

"We will not yield to these people," Bush said. "We will not yield to terrorists. We will find them. We will bring them to justice. At the same time, we will spread an ideology of hope and compassion that will overwhelm their ideology of hate."

A day after celebration

Less than 24 hours earlier, Londoners literally had danced in the streets to celebrate the city's surprise triumph over Paris in winning the right to host the 2012 Summer Olympic Games. But the jubilation was smashed in attacks that security police here had long predicted as inevitable.

Ken Livingstone, the mayor of London, still in Singapore where the Olympics decision was made, condemned what he called a "cowardly attack."

"This was not a terrorist attack against the mighty and the powerful," Livingstone said. "It was not aimed at presidents or prime ministers. It was aimed at ordinary, working-class Londoners, black and white, Muslim and Christian, Hindu and Jew, young and old. It was an indiscriminate attempt to slaughter, irrespective of any considerations for age, for class, for religion, or whatever."

The shutdown of the transit system after the blasts launched a long, confused commute later in the day for many Londoners. People accustomed to traveling on the Underground had to find their own way home. Many people shared rides in taxis. Others simply walked, leaving the sidewalks crowded while streets were unusually empty without the normal crush of double-decker buses.

"People are just blundering around. They're lost. They don't know where to go or what to do," said Phil Wended, a ruddy-faced newspaper salesman in rolled-up sleeves, hawking the Evening Standard in front of the shuttered Liverpool Street station. "They only know a few streets 'round the Tube. They've got no idea how to get home."

Information from The Washington Post is included in this report.