Nation responds in aftermath of deadly rush-hour terror attack.
LONDON -- Office workers wordlessly filled the streets, construction workers removed their hard hats and London's famous black cabs pulled to the side of the road as Britain paid a silent tribute to the victims of four terrorist bombs that struck a week ago Thursday.
Queen Elizabeth II stood motionless outside Buckingham Palace, and a crowd filled Trafalgar Square, where many could be seen wiping away tears and hanging their heads in prayer during the two-minute tribute that began at noon.
The silence was broken only by the tolling of Big Ben.
But the hush didn't mean there was a standstill in the investigation.
British and FBI officials focused on two more suspects -- an Egyptian-born chemist who studied in the United States and an 18-year-old Briton of Pakistani descent believed to have set off the bomb aboard a red double-decker bus.
Security forces in camouflage searched the Beeston area of the northern city of Leeds as police tried to crack the network thought to have given the dead suspects planning, logistical and bomb-making support.
"We don't know if there is a fifth man, or a sixth man, a seventh man or an eighth man," London's Metropolitan Police commissioner Sir Ian Blair told foreign journalists.
British authorities were seeking a Pakistani Briton with possible ties to al-Qaida followers in the United States, news reports said. They said he may have organized the attacks and chosen the targets, leaving Britain the day before the July 7 bombings.
"Al-Qaida is not an organization. Al-Qaida is a way of working ... but this has the hallmarks of that approach," Blair said of the attacks, which killed 54 people, including four bombers. "Al-Qaida clearly has the ability to provide training ... to provide expertise ... and I think that is what has occurred here."
FBI agents in Raleigh, N.C., joined the search for the chemist, Magdy Asi el-Nashar, a 33-year-old former North Carolina State University graduate student. The doors were locked Thursday at the building at Leeds University where he recently taught chemistry.
And in a further international development in the inquiry, Jamaica's government said it was investigating a Jamaican-born Briton as one of the bombers.
Hasib Hussain, 18, allegedly set off the bomb that killed 14 people aboard the bus. That blast occurred nearly an hour after three London Underground trains blew up, and investigators don't yet know what Hussain did during that hour or when he boarded the bus.
Trying to map out Hussain's movements, police appealed for information from anyone who may have seen him in or around King's Cross station, where the four suspects parted ways. They released a closed-circuit television image showing him wearing a large camping-style backpack as he strode through a train station in Luton, outside London, about 2 1/2 hours before he allegedly blew up the No. 30 bus. He had a mustache and wore jeans, a white shirt, and a dark zip-up top or jacket.
A separate photo of his face showed him with a beard, looking straight ahead.
"Did you see this man at King's Cross?" Peter Clarke, head of the Metropolitan Police anti-terrorist branch, asked in a televised appeal. "Was he alone or with others? Do you know the route he took from (King's Cross) station? Did you see him get on to a No. 30 bus?
Remembrances also took place around the world -- from terrorism-scarred sites in Madrid and the Indonesian resort island of Bali, to a British base in Afghanistan.
Authorities announced that the death toll from the July 7 subway and bus attacks had risen to 53, including the four suicide bombers.
In the northern city of Leeds, the home of at least two of the bombers, young Muslims paused in silence before speeches by local imam, a minister and community leaders.
Trucks, cars and mounted police all paused along the busy Euston Road outside King's Cross station, where a memorial garden has been a focus of the city's grief. Mayor Ken Livingstone laid a wreath there, and hundreds stood silently at the station near the worst of the attacks -- a subway train bombing that killed at least 21 people.
At the British Open in St. Andrews, Scotland, an airhorn signaled suspension of play and Tiger Woods took off his hat, closed his eyes and bowed his head at the 14th hole.
British TV interrupted normal broadcasting to show photos of the aftermath of the bombings: soot-faced commuters fleeing in fear and paramedics tending to the injured.
People across Europe also paused. In Madrid, Spain, which was hit by al-Qaida-linked train bombings that killed 191 people last year, Mayor Alberto Ruiz Gallardon and other officials observed the silence in a plaza outside town hall.
Sirens wailed across Paris, with French President Jacques Chirac and visiting Brazilian President Luis Inacio Lula de Silva standing at attention outside the Elysee Palace.
British, Afghan and American flags flew at half-staff at the main U.S. base in Kabul as about 200 U.S. and other troops stood silently for two minutes.
In Leeds, hundreds gathered in silence outside the Hamara Living Center, where one suspect counseled disabled youths.
"We condemn these terrorists and what they have done," said Munir Shah, imam of the Stratford Street mosque near the Leeds neighborhood police were searching. "Islam does not agree or teach about the killing of innocent people."