Multiple explosions rocked the London subway system and tore apart a double-decker bus Wednesday, in what British Prime Minister Tony Blair called a series of "barbaric" terrorist attacks. British officials say at least 33 are dead. Hundreds more are wounded.

A previously unknown group calling itself the Secret Organization of al-Qaida in Europe claimed responsibility for the attacks.

Injured tube passengers are escorted away from Edgware Road Tube Station in London following explosion, Thursday

The rush-hour explosions came as the G-8 summit, hosted by British Prime Minister Tony Blair, was beginning in Scotland.  One blast destroyed a double-decker bus near Russell Square.  Three explosions rocked the city's subway system, forcing officials to shut it down.

One passenger described her ordeal. “All of the windows came in and none of us knew what happened, and everywhere there was mayhem. And then the driver came out of the carriage, which was quite scary, because he shone a red light, and we all thought... well, I thought I was dead."

Speaking from Gleneagles, Scotland, a visibly shaken Prime Minister Blair said he was certain the attacks were timed to coordinate with the start of the G-8 Summit. He said the other G-8 leaders would continue the summit in his absence, while he returned to London.

And he had a message for those responsible for the attacks. "It's important however, that those engaged in terrorism realize that our determination to defend our values and our way of life is greater than their determination to cause death and destruction to innocent people, in a desire to impose extremism on the world."

Later, Mister Blair appeared with the other G-8 leaders and read a joint statement, condemning what he called the "barbaric" attacks.

Shortly after Mister Blair spoke, U.S. President George Bush offered his condolences to the British people. He said the other G-8 leaders shared his resolve to ultimately defeat terrorism.

"We will not yield to these people, we will not yield to the terrorists. We will find them, we will bring them to justice," said the president.

Various officials from other nations - including French Prime Minister Dominique de Villepin also issued statements of support.