LONDON — The death toll in London’s deadliest terrorist attack rose to more than 50 yesterday and appeared certain to climb higher as frantic families searched hospitals for loved ones still missing.
At the same time, authorities conducted perhaps the biggest manhunt in British history for the terrorist gang behind Thursday’s 56-minute spree of death during the morning rush hour.
Home Secretary Charles Clarke likened the manhunt to “looking for a small number of very evil needles in a very large haystack.”
Millions of wary but unbowed commuters returned to their jobs in the British capital yesterday, one day after bombs ripped through three subway trains and a double-decker bus.
Police said each of the four bombs weighed less than 10 pounds and discounted speculation that suicide bombers were involved.
Rescue workers dug through twisted, blood-spattered wreckage in search of the bodies that have yet to be added to the official death toll.
By late afternoon, the official figure stood at 49 dead, but “there are still a number of bodies” in a rail tunnel at one station, King’s Cross, and “we don’t know how many there are there,” said Metropolitan Police Commissioner Ian Blair.
Twenty-one persons already are known to have died at King’s Cross station.
Other bombs smashed trains at Aldgate station in East London and at Edgware Road in West London, and the double-decker bus, whose roof was torn away and at least 13 riders — some of them fleeing the rail stations — met their deaths.
Another 700 were luckier. They were injured in the explosions but survived, although 22 remained hospitalized in serious condition.
President Bush, back in Washington from a summit in Scotland, went directly to the British Embassy to sign the book of condolences for victims.
“For long we’ve admired the great spirit of the Londoners and people of Great Britain. And once again that great strength of character is coming through,” the president told reporters.
Local Muslim leaders also visited the British Embassy yesterday to offer condolences for the bombings.
Imam Johari Abdul-Malik, chairman of the Coordinating Council of Muslim Organizations, and Mahdi Bray, executive director of the Muslim American Society Freedom Foundation, led the group.
“It is with the deepest sympathy that I write to your excellency to convey my personal condolences for the tragic events of terrorism that have taken place on your soil,” Mr. Bray said in a letter delivered to British Ambassador David Manning.
In New York, the bell that was a gift to New York from the people of London after the 2001 terrorist attack rang in a tiny chapel near ground zero — this time with New Yorkers mourning those who died in Britain.
The 5-foot-high, 650-pound bell, known as the Bell of Hope, was given to New Yorkers on September 11, 2002. It was cast by London’s Whitechapel Bell Foundry, which also cast the Liberty Bell and London’s Big Ben bell.
For dozens of parents and spouses, sons and daughters, yesterday was a desperate quest for news of family members who haven’t been heard from since they headed off to work Thursday morning.
They zeroed in on hospitals and deluged police with thousands of phone calls for information.
The terrorists didn’t care who they killed, said Police Commissioner Blair. “This was an attack which was entirely arbitrary, random, irrespective of race, of color, or gender and age.”
Victims came not only from Britain, but also from Australia, Sierra Leone, Portugal, Poland and China, he added. At least four Americans were injured.
As the manhunt expanded, with ports and airports in a state of high alert and huge stacks of closed-circuit television material accumulating in police stations, the commissioner said it was “blindingly obvious” that a terrorist cell was at large in Britain.
Attention centered on a shadowy group that calls itself the “Secret Organization Group of al Qaeda Jihad Organization in Europe” and declared on a Web site Thursday morning that it had “carried out a blessed raid in London” and that “Britain is burning with fear, terror and panic.”
Mr. Clarke said that authorities, who at first had treated the claim with skepticism, were now taking it seriously.
Authorities said that reports of two unexploded bombs said to have been discovered on Thursday turned out to be unfounded.
Police anti-terrorist branch chief Andy Hayman said the devices used were deceptively simple — less than 10 pounds of an explosive in each bomb and something that could be carried in an ordinary knapsack.
Mr. Hayman said preliminary evidence indicated the bombs had simply been placed on the floor in one of the three front cars in each of the three trains — or in the case of the double-decker bus, on or under a rear seat.
An American security consulting firm that often works on State and Defense department projects yesterday called the bombing of the London double-decker bus “an anomaly among the four attacks.”
“The bus bombing, which occurred a full half hour after the last Underground attack, is another example of the need for extreme caution following any type of attack — because follow-up attacks meant to cause even more death and destruction do occur,” Strategic Forecasting Inc., also known as Stratfor, said in an intelligence briefing.
Although there were several theories on why terrorists targeted the bus — when the other three bombs hit London’s Underground commuter rail system — one explanation was that it was a secondary bomb meant to kill people fleeing the subway after the earlier explosions.
Mr. Blair, the police commissioner, said there was “absolutely nothing to suggest that this was a suicide bombing attack.”
Queen Elizabeth II, her son and heir-apparent to her throne, Prince Charles, and Charles’ wife, the Duchess of Cornwall, visited the injured at several London hospitals.
“Those who perpetrate these brutal acts against innocent people should know that they will not change our way of life,” the queen said.
Jerry Seper in Washington contributed to this article, which was based in part on wire service reports.