The bureau said it was searching for a 27-year-old Saudi, Adnan G. El Shukrijumah, who was "possibly involved with Al Qaeda terrorist activities and, if [that's] true, poses a serious threat to U.S. citizens and interests worldwide," according to a nationwide alert to law enforcement authorities.
On Thursday, law enforcement sources said, FBI agents were scouring a South Florida neighborhood believed to have been Shukrijumah's last known address in the United States. Agents already have interviewed the suspect's brother, who said that Shukrijumah had left the U.S. a number of years ago for Morocco, a source said.
The sources said the FBI had developed very preliminary information indicating that Shukrijumah may be a trained pilot or had attended flight school, possibly in Florida. But the sources emphasized that the information may turn out to be erroneous. Several of the 19 hijackers in the Sept. 11 terrorist attacks had Florida connections, and received flight training there.
In January, the FBI called off a nationwide manhunt that had triggered fears of a possible New Year's terrorist plot, after concluding that an informant was not credible. The FBI said Shukrijumah carries a Guyanese passport but may attempt to enter the United States with a passport from Saudi Arabia, Canada or Trinidad, and that he also is known to use several aliases.
"We believe he may pose a significant and imminent danger," a law enforcement official said.
On Monday, Department of Homeland Security officials raised the U.S. terrorism threat level to orange, indicating a high risk of terrorist attack. That followed weeks of intelligence-gathering indicating that the onset of war in Iraq could trigger so-called sympathy strikes by Al Qaeda against U.S. interests around the world.
It also comes as FBI agents around the country are stepping up efforts to interview and possibly detain Iraqi nationals who they suspect may be sympathetic to Iraqi President Saddam Hussein.
It wasn't clear what role any suspected activities by Shukrijumah may have played in the decision to heighten the alert, though officials previously indicated that several factors played a part, including growing "chatter" among potential terrorists picked up by authorities.
As the FBI sought help in locating Shukrijumah, it dropped a request it made early last month for help in locating a 36-year-old Pakistani, Mohammed Sher Mohammad Khan. An FBI spokesman said officials now believe information they had developed about Khan pertained to Shukrijumah.
The FBI said Shukrijumah is 5 feet 3 to 5 feet 5 and weighs 132 pounds. He has a Mediterranean complexion, black hair and black eyes, and occasionally wears a beard, the bureau said.
The FBI, which posted his photograph on its Web site, www.fbi.gov, said Shukrijumah has used the following aliases: Adnan G. El Shukri Jumah; Abu Arif; Ja'far Al-Tayar; Jaffar Al-Tayyar; Jafar Tayar; and Jaafar Al-Tayyar.