Federal prosecutors mindful of new terrorism warnings sought the identity Wednesday of a man charged with carrying fake identification on a road near the Pentagon. A judge ordered the man held.

"There is a substantial risk of the defendant's flight," U.S. Magistrate Judge Theresa Buchanan said of the man, identified in court papers as "Imad Abdel-Fattah Hamed, aka Imad Nimer."

A criminal complaint filed by the FBI revealed that Hamed was interviewed previously by the agency, on Oct. 22. An FBI supervisor, Steve Berry, would not elaborate on the initial interview.

Just hours after the FBI issued a terrorist alert Monday night, Hamed and another man were detained by state and federal law enforcement officials as Hamed drove a tow truck on Route 110, which passes close by the Pentagon. The route was closed to commercial and other big vehicles after the Sept. 11 terror attacks, one of which tore a hole in the side of the Pentagon and killed 189 people.

According to the FBI complaint, state police found a variety of driver's licenses and other false government-issued documents. The men offered several explanations for why they were there and where they were going, the complaint said.

"Their motivations are still unclear," Virginia State Police spokeswoman Lucy Caldwell said.

The mystery rattled law enforcement and other government officials who have been on high alert since the Pentagon and the World Trade Center attacks. Monday night, the FBI issued its latest terror alert, warning of an unspecified attack possibly as early as Tuesday.

"The timing of this apparent attempt to breach security, after the latest FBI warning of a specific and credible terrorist threat, certainly gives me pause," Virginia Gov. Mark Warner said in a statement.

There was no indication of a connection between the men and 17 named Monday by the FBI as possible conspirators in a terror attack thought planned for this week. A Justice Department official said a check of immigration records showed no indication any the 17 ever have been in the United States.

Law enforcement officials also were investigating whether the two caught at the Pentagon are linked with known terrorists or terrorist cells but had found no connection by late Wednesday night, a knowledgeable official said, speaking on condition of anonymity.

After questioning by the FBI, the passenger in the truck Hamed was driving was turned over to the Immigration and Naturalization Service. He was detained and was not identified publicly.

Meanwhile, federal law enforcement authorities took custody of Hamed, who appeared Wednesday at the U.S. District Courthouse in Alexandria, Va.

He is charged with committing identification document fraud and making false statements, which carry on conviction a sentence as high as 15 years in jail, according to prosecutor John Morton.

"We are busily engaged in determining what Mr. Hamed's true identification and true nationality is," Morton said.

Hamed, clad in a white short-sleeved shirt and black jeans and wearing a mustache and beard, asked Buchanan what to do about his job and said he could afford a lawyer before being led away. Buchanan set a preliminary hearing for Friday.

Traveling south on Route 110 about 10:30 p.m. Monday, the tow truck drove past signs erected in November that prohibit commercial vehicles on the road, according to the complaint.

Officers in a police cruiser who watched the truck go by alerted a second team stationed farther along the road.

The second team questioned the driver and passenger, "both of whom appeared to be Middle Eastern males," according to the complaint, and found several false driver's licenses and other government documents inside. Several of the documents bore pictures matching those of the driver and passenger but had conflicting addresses, dates of birth and Social Security numbers.

The truck bore a Virginia inspection sticker and temporary Maryland tags, the complaint said.

FBI dogs searched the truck for weapons and explosives but turned up none, Caldwell said.