More than 30 die in London blasts
Passengers evacuate an underground train at Kings Cross (Photo: Alexander Chadwick)
A series of bomb attacks on London's transport network have killed more than 30 people and injured scores more.
There were three explosions on the Underground - which police said left 33 dead - and one on a double-decker bus in which an unknown number died.
UK Prime Minister Tony Blair, who has returned to London from the G8 summit, has described the attack as "barbaric".
An Islamist website has posted a statement - purportedly from al-Qaeda - claiming it was behind the attacks.
Map of where the blasts happened
US President George Bush told reporters at the G8 Summit in Gleneagles that "the war on terror goes on."
The Queen said she was "deeply shocked" and sent her sympathy to those affected.
Home Secretary Charles Clarke said the blasts occurred between Aldgate East and Liverpool Street tube stations; between Russell Square and King's Cross tube stations; at Edgware Road tube station; and on a bus at Tavistock Square.
It's particularly barbaric that this has happened on a day when people are meeting to try to help the problems of poverty and Africa
Blair statement in full
Bus 'ripped apart'
Blast locations in detail
"We will not yield to these terrorists, we will find them, we will bring them to justice," he said.
Paul Woodrow, of the London Ambulance Service, is in Russell Square near the bus which exploded.
"At King's Cross station there is a rescue operation in the tunnel down on the line," he said.
"Although we cannot confirm casualties - it is too early - we are dealing with large numbers of casualties."
Metropolitan Police Deputy Assistant Commissioner Brian Paddick confirmed 33 people had died in the blasts on the Underground. He said it was not yet known how many died in the bus blast.
In other developments:
The officer in charge of policing the G8 summit said many of the 1,500 Metropolitan Police officers in Scotland would be urgently redeployed to London
New Olympics minister Tessa Jowell said celebrations to mark the homecoming from Singapore of the successful London Olympic bid team have been cancelled
Pope Benedict said the blasts were "barbaric acts against humanity" in a message to the Archbishop of Westminster Cardinal Cormac Murphy O'Connor
54 state schools were closed in Westminster
Mobile phone services across London were jammed with all major networks reporting problems as people tried to contact relatives and friends. A spokeswoman for Vodafone said the emergency services were being given priority.
Some 208 casualties were taken to the Royal London Hospital in Whitechapel, with 26 people admitted - 13 are in theatre and another three are in intensive care.
The city's St Mary's Hospital said it was dealing with 26 injured people, including four with critical injuries and eight in a serious condition.
People were screaming and shouting and saying things like I'm dying, I'm dying, please help me.
Liverpool Street Station
Mr Paddick confirmed police were looking into whether the bus blast was the work of a suicide bomber.
But, he added: "It could as easily be an explosive device left on the bus as the work of a suicide bomber. We are not able to determine which it was yet."
London police chief Sir Ian Blair urged people to stay where they were and not to call emergency services unless it was a life-threatening situation.
He reassured the public that an emergency plan was in place and the situation was "steadily coming under control".
London Mayor Ken Livingstone, speaking from Singapore before flying back to the UK, said Londoners would not be divided by a "cowardly attack".
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There are a lot of people phoning loved ones to make sure they are ok
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He said it was an "indiscriminate" attempt at slaughter with no consideration for age or religion.
All London Underground services have been suspended indefinitely and bus services in central London (Zone One) have been halted.
Early reports had suggested a power surge could be to blame for explosions on the Underground but this was later discounted.
Describing the bus blast in Tavistock Square, witness Belinda Seabrook said she saw an explosion rip through the vehicle.
"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," she said.
She said the bus had been travelling from Euston to Russell Square and was "packed" with people turned away from Tube stops.
"It was a massive explosion and there were papers and half a bus flying through the air." she said.
One caller to BBC Five Live said his friend had seen "the bus ripped open like a can of sardines".