Blasts Rock London Transit System

(CBS/AP)  A series of deadly explosions rocked the London subway and tore open a packed double-decker bus during the morning rush hour Thursday in what a shaken Prime Minister

Tony Blair (video)

called a "barbaric" terrorist attack.

British officials confirmed two deaths, but a U.S. law enforcement official said at least 40 people were killed in the blasts. The U.S official spoke on condition of anonymity because British officials have yet to make public the death toll.

London hospitals reported more than 300 people were injured.

Blair said it was clear the attacks were designed to coincide with the opening of the G-8 summit in Gleneagles, Scotland. The prime minister left the summit to return to London, but said the deadly explosions would not halt the work of the annual meeting.

"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 in a statement on behalf of the Group of Eight leaders. "We will continue our deliberations in the interest of a better world," he said a day after London was awarded the 2012 Olympics.

President Bush offered his condolences to the British people after the blasts. "The war on terror goes on," Mr. Bush said. He warned Americans to be "extra vigilant" as they head to work.

Top U.S. counterterror officials said there were no plans to increase the current alert status. The Homeland Security Department said there are also no indications of an imminent attack on U.S. interests. A Homeland Security official told CBS News the government's "interagency incident management group" is meeting to "assure full situational awareness."

Britain's Home Secretary Charles Clarke said there were three explosions in the subway and one on a bus. A senior police official said traces of explosives were found at two explosion sites.

Police reported "a number of fatalities" at one London subway station. "Things are still relatively confused," Superintendent John Morgan told reporters.

Officials at seven major hospitals surveyed by The Associated Press reported that 334 people had been wounded, including more than 120 who were treated and released. Police said 150 had been seriously injured.

A group calling itself ``The Secret Organization of al Qaeda in Europe'' posted a claim of responsibility for the blasts, saying they were in retaliation for Britain's involvement in Iraq and Afghanistan. The Web statement, republished on the site of the German magazine Der Spiegel, could not be immediately confirmed.

Bloodied and bandaged witnesses (video)

reported panicked crowds fleeing the blast sites. A witness at the bus explosion said the entire top deck of the bus was destroyed.

"It was chaos," said Gary Lewis, 32, who was evacuated from a subway train at King's Cross station. "The one haunting image was someone whose face was totally black and pouring with blood."

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