( AP ) - Police mounted increased patrols in a jittery London Saturday as detectives conducted an intense hunt for a man seen running from an explosives-packed car in the heart of the city's entertainment district.
Two Mercedes loaded with gasoline, gas canisters and nails were found abandoned Friday in what police believe was an attempt to kill scores or even hundreds of people. Detectives said they were keeping an open mind about the perpetrators, but terrorism experts said the signs pointed to an al-Qaida-linked or inspired cell.
Scotland Yard would not comment on a report by ABC News in the United States that police had a "crystal clear" picture of one suspect from CCTV footage.
Forensics experts were searching the two cars for clues. One was abandoned outside a nightclub in Haymarket, a busy street of shops, clubs and restaurants just yards from Trafalgar Square and Piccadilly Circus.
The other was towed after being parked illegally in nearby Cockspur Street and was discovered in an impound lot about a mile away in Park Lane, near Hyde Park.
Deputy Assistant Commissioner Peter Clarke, the Metropolitan Police anti-terrorism chief, said the two devices could have caused "significant injury or loss of life."
"The discovery of what appears to be a second bomb is obviously troubling, and reinforces the need for the public to be alert," he said.
The plot rattled London a week before the second anniversary of the July 7 suicide bombings that killed 52 commuters on the city's transit system, and two days after Prime Minister Gordon Brown took office.
" London on the Edge" said the front page headline in The Independent newspaper on Saturday, while the Daily Mail asked, "Where's the Next Bomb?"
Brown urged people to be alert, saying Britain faced "a serious and continuous security threat."
The Times newspaper reported that police had distributed a document to nightclubs two weeks ago warning of the threat from "vehicle-borne explosive devices" - car bombs. The document, prepared by the National Counterterrorism Security Office, took the form of general counterterrorism advice for British clubs.
The government's crisis committee, code-named COBRA, was due to meet Saturday and police said they were strengthening patrols in the city to reassure the public.
Tens of thousands of people were expected to march through central London later Saturday in the city's annual Gay Pride parade, which ends at Trafalgar Square.
Terrorism experts said the improvised devices discovered Friday were similar to ones used by homegrown terror cells - much like the bombs used in the July 7 attacks - although the discovery of the second device suggested a coordinated and more sophisticated attack.
Intelligence officials were examining a post on an Islamist Web site hours before the cars were found suggesting Britain would be attacked for awarding a knighthood to novelist Salman Rushdie and for intervening in Muslim countries.
The U.S.-based SITE Intelligence Group, which monitors extremist Web sites, said a post on the al-Hesbah forum asked, "Is London craving explosions from al-Qaida?" and added: "I say the good news, by Allah, London will be hit."
SITE said the message had been posted to an unmoderated, public section of the forum, and its relationship, if any, to the car bombs could not be verified.
The first bomb was discovered after ambulance crews were called to Haymarket to treat a man injured in a fall at 1:30 a.m. Friday. When crews arrived, they noticed smoke coming from a green Mercedes parked in front of a club, Clarke said.
Photographs showed a canister bearing the words "patio gas," indicating it was propane, next to the car. The back door was open with blankets spilling out. The car was removed from the scene after a bomb squad disabled the explosives.
Sky News television reported that a police officer seized a telephone from the first car - believed to have been a potential detonator - and an American lawmaker briefed on the investigation confirmed British authorities had found a cell phone.
"They found a cell phone, and it was going to be used to detonate the bomb," Congressman Peter King, a Republican representing New York.
Police would not comment on the claim.
Around 3:30 a.m., a second car parked on nearby Cockspur Street, which runs between Haymarket and Trafalgar Square, was ticketed and then towed to a lot on Park Lane, Clarke said. Police closed off Park Lane, reportedly after attendants smelled gasoline. Clarke said police were examining footage from closed-circuit TV cameras, hoping the surveillance network in central London would help them track down the drivers of the Mercedes.
The CCTV footage will be compared with license plate recognition software, he said.
There had been no prior intelligence of planned al-Qaida attacks, a British government official told The Associated Press on condition of anonymity because of the sensitivity of the investigation.
A British security official said the domestic spy agency MI5 would examine possible connections between the bomb attempt and at least two similar foiled plots - to attack a London nightclub in 2004, and to pack limousines with gas canisters and shrapnel. In the 2004 plot, accused members of an al-Qaida-linked terror cell were convicted of plotting to blow up the Ministry of Sound nightclub, one of London's biggest music venues.