The FBI passed on the warning about Mohammed Sidique Khan to British authorities before the July 7 bombings, two U.S. law enforcement officials based in New York said Tuesday.
The informant, Mohammed Junaid Babar, identified Khan as a potential terrorist, said the officials, who spoke on condition of anonymity because the investigation is based in Britain. However, they said, Babar offered no specific information about a plot targeting the transit system.
Khan and fellow bomber Shehzad Tanweer were briefly put under surveillance by Britain's MI5 security agency in 2004, but the operation was halted when security services decided the men did not pose any immediate threat. They were among four men who later blew up three subways and a double-decker bus, killing 52 commuters and themselves.
Khan, a 30-year-old Briton of Pakistani descent, reportedly had traveled to Pakistan. In a videotape that surfaced after the bombings, he said he was inspired by al Qaeda leader Osama bin Laden.
Babar, a U.S. citizen of Pakistani descent, has pleaded guilty to terrorism charges in federal court in Manhattan. In his plea agreement, he described traveling to the Pakistani province of Waziristan to supply cash and military equipment to al Qaeda and providing members of the Pakistani terror cell in London with material for fertilizer bombs.
A scheme to blow up pubs, restaurants and train stations was foiled in March 2004, when British authorities arrested several suspects and seized 1,000 pounds of ammonium nitrate from a storage locker in London. Babar, who remains in custody in New York, is due in Britain later this month to give prosecution evidence at the trial of seven men charged in the plot.
Britain's Home Office and London's Metropolitan Police have refused to comment on Babar's claims about intelligence related to Khan, citing government policy not to discuss issues of security or intelligence.
The British government is to publish at least part of a review of intelligence on the July 7 bombings after Home Secretary Charles Clarke called for a narrative of events leading to the bombings.