Terrorism came to London at the morning rush hour in the shape of a series of explosions that killed and maimed people across the capital.
Authorities now say 37 people were killed and 700 injured in the bombs that ripped through three subway trains and a double-decker bus, Thursday.
Meanwhile, one U.S. law enforcement official says he has been told by British authorities the death toll is at least 40.
The apparently coordinated explosions were aimed at the London transportation system, at a time of day when upwards of three million men and women are making their way to work. And the British government had no doubt who was to blame, saying a band of terrorists, probably from Osama bin Laden's al-Qaida organization.
Prime Minister Tony Blair, in a nationwide television address within hours of the explosions, said "It is reasonably clear that there have been a series of terrorist attacks" in downtown London, an outrage that he described as "barbaric."
Police say residue from explosives have been found at two of the blast sites, and a former anti-terrorist squad chief, John Stalker, says the attacks bear all the hallmarks of an al-Qaida operation. A previously unheard of terrorist group calling itself the "Secret Organization: al-Qaida in Europe" claimed responsibility for the bloodshed.
The death and destruction brought carnage and chaos to the heart of one of the world's busiest capitals. A series of explosions at underground rail stations brought that city's entire system to a standstill for hours. Eyewitnesses reported seeing bodies piled in the wreckage of one train.
Some commuters fled one station and climbed aboard a double-decker bus, only to be trapped when a massive explosion blew the vehicle apart, ripping off its roof. Eyewitnesses reported numerous deaths in the bus blast.
A spokesman for London's ambulance service, Paul Woodrow, said "we believe there are a number of fatalities" in the explosions. Some of the injured were loaded onto other double-decker buses, to be taken to hospitals that rapidly became jammed.
London has undergone a series of terrorist alerts since the September 11 terrorist attacks on New York and the Pentagon in 2001, but there were no indications of any advance warning of the bombings.
Police also were investigating the possibility that the attacks are linked to the Group of Eight meeting that brought together the heads of the world's largest industrial nations and Russia beginning Wednesday in Gleneagles, Scotland. That conference has been dogged by violence involving hundreds of protesters.
It was at the G-8 meeting that Prime Minister Blair received word of the London attacks. He immediately flew back to the capital to take charge, but he said the Gleneagles conference would go on.
What he returned to was a city stunned by a major terrorist onslaught that forced its underground rail system to shut down within minutes. Hours later, it was still closed, while rescue teams dug out the injured and the dead.