Terrorism experts said the improvised devices discovered Friday were similar to ones used by homegrown terror cells _ including the bombs used in the July 7 attacks _ although the discovery of the second device suggested a coordinated and more sophisticated attack, possibly a terror cell with links to al-Qaida in Pakistan.
Intelligence officials were examining a post to an Islamist Web site _ hours before the cars were found _ that suggested Britain would be attacked for awarding a knighthood to the 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.
U.S. Rep. Peter King, R-N.Y., was briefed on the investigation and confirmed British authorities had found a cell phone.
"They found a cell phone, and it was going to be used to detonate the bomb," King said Friday.
Police would not comment on the claim.
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.
