LONDON -- Home Secretary Charles Clarke, Britain's top law enforcement officer, said a series of blasts across London today have yielded "terrible injuries."

An explosion destroyed a double-decker bus in central London during rush hour Thursday, police said, and several blasts also went off on the London subway. London's police chief said there are signs of explosives at the site of one of today's blasts. Police have reported "a number of fatalities" at one London subway station.

The nearly simultaneous explosions came a day after London was awarded the 2012 Olympics and as the G-8 summit was getting under way in Scotland.

"It’s recently clear that there have been a series of terrorist attacks in London. There are obviously casualties, both people that have died and people seriously injured. My thoughts and prayers are with the victims and their families," British Prime Minister Tony Blair said.

Blair is hosting the world's most powerful leaders at Gleneagles, Scotland.

“It's my intention to leave the G8 within the next couple hours and get a report from those who have been dealing with this,” Blair said. But he plans to return later this evening.

All the leaders decided that the meetings should continue in Blair's absence.

"Each of the countries around that table have some experience of the affects of terrorism and share our complete resolution to defeat this terrorism," Blair said. "It's particularly barbaric that this has happened on the day when people are meeting to try to help the problems of poverty in Africa and the long-term problems of changes in the environment."

"It's recently clear that it is designed and aimed to coincide with the opening of the G8. There will be time to talk later about this. 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," Blair said. "Whatever they do, it is our determination that they will never succeed in destroying what we hold dear in this country and in other civilized nations throughout the world."

A senior Israeli official said Scotland Yard told Israel minutes before the explosions that it had received warnings of possible terror attacks. But Israel's foreign minister is denying his country received a warning about possible terror attacks in London.

Italy's European commissioner, Franco Frattini, called the explosions a terrorist strike, the Apcom and ANSA news agencies reported. London's police chief said he was concerned they were a coordinated attack, but he said he wouldn't speculate on who was responsible.

Police said there have been at least six explosions in London. They also said at least two people died There were at least 95 people injured, CNN reported.

The first explosion was reported at 8:50 a.m. London time, 3:50 a.m. Eastern Time.

People covered in blood stumbled out of the subway, and a witness said the entire top deck of the bus was destroyed.

"I was on the bus in front and heard an incredible bang, I turned round and half the double-decker bus was in the air," Belinda Seabrook told Press Association, the British news agency.

She said the bus was packed with people.

"It was a massive explosion and there were papers and half a bus flying through the air," she said.

Officials shut down the entire underground network and the entire bus system after the explosions. Initial reports blamed a power surge, but officials were not ruling out an intentional attack.

Witness William Chamberlain said there were multiple casualties and multiple bodies strewn about the scene of the bus explosion. He said the bus was "torn apart like a tin can."

A London police spokesman appealed for calm, saying at the moment it's too early to judge what happened. He said what is needed is calm and as little media speculation as possible.

One witness, Darren Hall, said some passengers emerging from an evacuated subway station had soot and blood on their faces. He told BBC TV that he was evacuated along with others near the major King's Cross station and only afterward heard a blast.

The entire cell phone system has crashed in London.

Meanwhile, in the United States, the Washington, D.C., Metro system said it stepped up security immediately after an explosion on the subway system in London Thursday morning. Metro spokeswoman Candace Smith said passengers should expect to see increased police patrols, bomb- sniffing dogs and officers carrying machine guns. There have not been any reports of direct threats to the subway system.