More than 50 people were killed in yesterday's terror attacks in London, Metropolitan Police Commissioner Sir Ian Blair said today.
Sir Ian said there was "great difficulty in determining how many fatalities" because of the damage at scenes of the bombs blasts on the rush hour Tube and a bus.
He revealed that there were 700 casualties, 350 people were taken to hospital, 22 were still in a critical condition and one person died in hospital.
The commissioner said that the casualty bureau had already received 104,000 calls.
He said there was "absolutely nothing to suggest that this was a suicide bombing attack although nothing at this stage can be ruled out".
He agreed that the attack "bore all the hallmarks" of an al Qaida operation.
Anti-terrorist branch head Andy Hayman said each of the bombs contained less than 10lbs of high explosives and they were probably placed on the floor of the three Tube trains or, in the case of the bus, on the floor or a seat.
Sir Ian said it was open to question whether the terror cell responsible for the attack was still in the UK.
But he added: "We must remain vigilant."
The two men leading the manhunt for the bombers were speaking as defiant Londoners returned to the Tube and the buses today determined to carry on with their lives.
Although there were fewer commuters than usual, hundreds of thousands of people made their daily journeys into a city which still bore the scars of yesterday's co-ordinated terror attacks.
As the capital prepared to mark the 60th anniversary of the end of World War II this weekend, there was the same resolve that life would go on whatever the terrorists had hoped to achieve.
Home Secretary Charles Clarke said all efforts were being concentrated on catching the bombers to stop them striking again.
"The number one purpose today is to identify the perpetrators and arrest them because there is obviously a danger if there is a group that has committed these attacks not brought to justice and therefore able to continue thinking about carrying out further attacks.
"That is, of course, the number one preoccupation the police and security services have at this moment," he said.
He said the Government was taking seriously a claim on a website from an al Qaida group that it was responsible.
The Home Secretary defended the decision to lower the level of security threat in the capital before the attacks, saying that all the security services thought the risk had got "slightly lower".
"Obviously it was wrong. We have looked very carefully at the threat we are now under, particularly in the light of events yesterday, and the threat level will be increased."
He agreed that the authorities had "absolutely no idea" yesterday's attacks were being planned.
But he denied claims that London's security had been compromised because of Metropolitan Police officers being deployed to the G8 summit in Scotland.
Tony Blair, who has vowed that the culprits would be brought to justice, was expected to return to London later today after the final session of the G8 summit in Gleneagles.
The largest atrocity in peacetime London began at 8.51am yesterday when seven people died following the first blast in a Tube tunnel 100 yards from Liverpool Street Station.
At 8.56am, a blast in a tunnel between King's Cross and Russell Square left 21 people dead.
At 9.17am, seven people died after an explosion ripped through a tunnel wall at Edgware Road station, damaging three trains.
At 9.47am a blast tore the roof off of a red number 30 double decker bus packed with commuters forced above ground after the Tube network had been shut down.
Scotland Yard said two people were confirmed dead in the bus blast but eyewitnesses spoke of seeing more bodies.
An operation was today under way to recover the bodies of the 21 people who died close to King's Cross station.
Chief Superintendent Willie McCafferty, British Transport Police commander at King's Cross station, said: "That operation will take as long as it takes.
"Anti-terrorist squad officers are searching the scene and gathering evidence.
"I would think it would be at least two days before investigations are complete and the station is able to reopen."
The National Co-ordination Centre confirmed that the bodies of all of the dead are to be moved to London mortuaries by noon.
The Queen and the Prince of Wales were today visiting people caught up in the bomb tragedy.
Scotland Yard said there would be an increased visible police presence across the capital today.
Extra patrols will include officers from the Met, City of London Police and British Transport Police.
A spokesman said: "The officers are there to assist and reassure the public, particularly in communities where people may feel vulnerable at this time, and are not a response to any specific threat.
"We are encouraging the public to remain vigilant and to report any unattended items or suspicious activity to transport staff or the police."
Less than 24 hours after the capital came under attack, and despite continued disruption to the Tube network, many people made clear they would not let their lives be affected.
Sonia Crosby, station manager at Reading, Berkshire, said passengers were in "resilient" mood.
She said: "People are wanting to get back to normal. It won't stop anyone going back to work and that's what makes Great Britain great really."
Commuters arriving at King's Cross walked past police with sniffer dogs patrolling the concourse.
William Austin, who lives near Royston, Hertfordshire, said: "You have to carry on.
"People of my generation have grown up with the IRA threat and we've seen all sorts of bombings down the years.
"You just have to get on with life. The City will be up and running again today and these people won't have any effect."
Commuters were also back on the number 30 bus route this morning - a day after it delivered a devastating cargo into the heart of London.
Though some admitted trepidation and others nervously eyed fellow travellers and their luggage, most were simply glad of a means to travel to the city centre and return to some sense of normality.
Network Rail worker Gary Hoffman, 52, said he had little unease about this morning's journey.
"I'm not nervous at all about coming on this particular bus. We have to get into work and it looks as though the situation is under control," he said, sitting by the stairwell on the lower deck.
London was thrown into chaos in the wake of yesterday's blasts with shops, banks and offices closing and thousands of people left stranded on the streets as mainline stations were shut and Tube and bus services cancelled.
Anti-terrorist detectives are investigating the possibility that Britain was subjected to its first suicide bombing after the series of co-ordinated no warning strikes in the centre of the city.
Bus passenger Richard Jones, 61, an IT consultant, said he saw a man in his mid-20s on the bus become "extremely agitated".
Mr Jones, who left the bus seconds before it exploded, told the Daily Mail: "This chap started dipping down into his bag and getting back up. He did it about a dozen times in two or three minutes and looked extremely agitated."
The Archbishop of Canterbury, Dr Rowan Williams, today urged the country to "take courage" in the face of the terrorist attacks on London.
"The only finally adequate response to terror and evil is to gather ourselves... to reach down into what feeds the roots of our spirit, trusting that justice, mercy and joy are never going to be silenced or paralysed.
"And when we know that, we are ready to begin again on the long road of the long task of making humanity really human," he said as he delivered BBC Radio 4's Thought For The Day.
Scotland Yard has issued a casualty hotline number on 0870 1566 344.