LONDON (Reuters) - Rescue workers inched through dangerous rail tunnels deep under London on Friday to hunt for clues and retrieve bodies after suspected al Qaeda bombers killed more than 50 people in rush-hour blasts.
Fears of more attacks and false alarms kept commuters and financial markets jittery, while authorities worldwide went on alert following threats to countries which, like Britain, have troops in Iraq.
A day after four bombs tore through three underground trains and a double-decker bus, the capital slowly got back to work. Many people took the day off, but others ventured back onto London's creaking transport network, some fearful, many defiant.
"No one's going to stop me going where I want to go in my own city," said shop worker Stuart Mills, 27. "You know what British people are like. They'll just carry on."
Mayor Ken Livingstone said the city would soon bounce back, noting it had been a week of "triumph and tragedy" for the capital, awarded the 2012 Olympics the day before the bombings.
The attacks -- which ministers said bore the hallmarks of the Islamic militant al Qaeda network -- were London's deadliest in peacetime and disrupted a summit of the leaders of the Group of Eight (G8) industrialised countries in Scotland.
Prime Minister Tony Blair briefly left the summit to attend a crisis meeting in London on Thursday but vowed not to let the attacks derail the meeting and announced on Friday that the G8 had agreed to boost aid for developing nations.
"We offer today this contrast with the politics of terror," he said. "It is hope that is the alternative to this hatred."
"EXTRAORDINARY HORROR"
Police chief Ian Blair said more than 50 people were killed in the blasts and 700 wounded, with 22 still critical.
He said people of many nationalities and religions had been caught up in the blast, noting the wounded were from countries including Australia, China, Poland, Portugal and Sierra Leone.
He said the death toll could rise further as police had yet to recover bodies from one of the bombed underground carriages, where rescue workers were encountering conditions of "extraordinary horror".
The bomb that tore off the roof of a bus killed 13 people, he said, compared to an initial death toll of two on the bus. It was not immediately clear if the 13 were included in the toll of 50 announced earlier in the day.
Desperate people hunted for missing relatives at hospitals, while others issued appeals for information. Commuters left flowers and notes at one of the bombed stations.
"To all the families and friends of those that died and were injured here yesterday, my thoughts and prayers are with you all. From a survivor. One of the lucky ones. William," read one.
Police chief Blair said the blasts bore all the hallmarks of al Qaeda but they did not suspect suicide bombers. Investigators were examining a claim of responsibility from the "Secret Group of al Qaeda's Jihad in Europe" over the war in Iraq.
The chief said more than one person carried out the attacks and those responsible were either at large in Britain or elsewhere or were dead.
"We have made no arrests so far," he said.
At Friday prayers across the capital, Muslims mourned the dead and, condemned the bombers but expressed fears of a backlash as the Muslim Council of Britain representing the country's 1.6 million Muslims was deluged with abusive messages.
TRAPPED BODIES
The police said no survivors were trapped underground and the task now was to retrieve bodies. One police source said there could be more than 10 bodies still underground.
Spain, hit last year by train bombings linked to al Qaeda which killed 191 people died, said it had sent security experts to Britain to help with the investigation. Spain withdrew its troops from Iraq after the bombings.
Andy Hayman, of the London police specialist operations branch, spoke of the "extreme circumstances" under which rescue services were working, saying they faced the hazards of tunnel collapse, vermin and "dangerous substances" in the air.
A maintenance worker, who did not want to be identified, said he had reached the site early on Friday and described "awful" scenes, with several bodies in the carriage.
"We got up to the carriage, although it was very dark there at the time," he told Reuters. "The smell was awful."
Hayman said each of the bombs was believed to have contained up to 10 lbs (4.5 kg) of explosives and could have been carried around in backpacks. The New York Times said timing devices rather than bombers set off the bombs.
An Internet statement from a group calling itself the "Organisation of al Qaeda - Jihad in the Arabian Peninsula" praised the attacks and said Rome would be targeted next.
The blasts battered financial markets on Thursday, but oil prices recovered to head back towards record highs near $62 on Friday as analysts said the attacks were expected to have a limited impact on the global economy and oil demand. British shares also recouped their losses, but sterling slid further.
