Terrorists: Britain 'burning with fear'

As investigators hunt those responsible for the London bombings, police are warning the death toll will pass 50.

London police chief Sir Ian Blair said the final toll was not known because of the dangers of reaching some of the underground blast sites. More than 50 people were killed, he said, and 700 wounded.

Out of the casualties 350 were taken to hospital and 22 are in a serious or critical condition.

Police have yet to reach one of the bombed tube carriages, and police sources said there could be more than 10 bodies still trapped underground.

A day after four bombs tore through three underground trains and a red double-decker bus, commuters headed to work again on London's battered transport network. Travellers on the Underground faced further disruption as the city was hit by a wave of station closures, triggered by reports of suspicious packages, all of which turned out to be false alarms.

Investigators scrambled to hunt down suspected al Qaeda bombers responsible for the attacks, the deadliest to strike London in peacetime.

Cabinet ministers said forensic teams were hunting for clues on who carried out the bombings and whether suicide attackers were involved.

The New York Times reported that timing devices rather than suicide bombers set off the explosions. The newspaper also cited unnamed US and British officials as saying the device which tore the top off the bus might have exploded prematurely as a bomber was carrying it to another target.

Andy Hayman, of the London police specialist operations branch, said the bombs were believed to have contained about 4.5kg of explosives and could have been smuggled onto the trains and the bus hidden in backpacks.

Sir Ian said: "We have absolutely nothing to suggest that this was a suicide bombing attack, although nothing at this stage can be ruled out."

However, Home Secretary Charles Clarke earlier said investigators were also looking into whether a suicide bomber had caused the fourth blast, which destroyed the bus.

Passengers on a number 30 bus, which had its roof torn off by a blast, reported seeing a dark-skinned man in his mid-20s rummaging in a bag seconds before the Tavistock Square explosion.

"I was standing next to a young gentleman who kept diving into a bag," said 61-year-old project manager Richard Jones.

Mr Clarke told BBC radio that investigators were examining a statement from the "Secret Group of al Qaeda's Jihad in Europe".

The email statement by the previously unknown group said: "Our mujahideen have carried out a blessed invasion in London and here is Britain now burning with fear and terror ... We have repeatedly warned Britain and have kept our promise."

Clarke said: "We monitor now very intensively a wide range of websites ... and this one and their claim is something we certainly take seriously."

But he said, "The fact is, we're looking for a very small number of very evil needles in a very large haystack, which is the City of London."

An internet statement from another group said Rome would be targeted next.

Prince Charles and his wife, the Duchess of Cornwall, yesterday visited victims of the bombings in hospital. "What I can never get over is the resilience of the British people who have set us all a fantastic example of how to react to these kinds of tragedies," he said.

The New Zealand Ministry of Foreign Affairs and Trade said last night that it had serious concerns about a lack of contact from a New Zealander believed to have been in London.

- AGENCIES