WASHINGTON -- Pointing toward other potential terrorist threats, the Justice Department says that about 20 people have been charged since the Sept. 11 attacks with fraudulently obtaining licences to transport hazardous materials.

Declaring that terrorism "is a clear and present danger to Americans today," Attorney General John Ashcroft said Tuesday that some people who sought such licences may have links to the hijackers of the four planes that crashed in New York, Washington and Pennsylvania, killing thousands.

"Intelligence information available to the FBI indicates a potential for additional terrorist incidents," the attorney general told Congress.

Since the attacks, about 20 people have been charged with fraudulently obtaining licences to transport hazardous material, said a senior Justice Department official, who spoke on condition of anonymity. He declined to elaborate.

Meanwhile, a Virginia man whose name and phone number were found in a car registered to one of the 19 suspected hijackers was charged with forgery earlier this week, according to unsealed court records.

Mohamed Abdi of Alexandria, Va., was charged with forging his landlord's signature on housing subsidy cheques he was receiving from Arlington County and cashing the cheques. A detention hearing was scheduled Wednesday.

Investigators said the name "Mohumed" and a phone registered to Abdi was written on a Washington road map found inside a car parked in a lot at Dulles International Airport, where American Airlines flight 77 was hijacked. The plane, a Boeing 757, smashed into the Pentagon.

The car, found the day after the hijackings, was registered to Nawaq Alhamzi, identified by the FBI as one of the hijackers of the American flight, the records said. The FBI also found a cashier's cheque made out to a flight school in Phoenix; four drawings of the cockpit of a 757 jet; a box-cutter-type knife; and maps of Washington and New York.

Nabil Al-Marabh, 34, a former Boston cab driver taken into custody in Chicago last week by investigators, holds a commercial driver's licence and is certified to transport hazardous materials. Al-Marabh has been moved to New York for questioning.

The focus on trucks with hazardous materials follows disclosures that Mohamed Atta, suspected of piloting one of the two hijacked passenger airliners that struck the World Trade Center, was interested in farm crop-dusting planes. Ashcroft said the FBI had gathered information, raising fears that agricultural aircraft could be used in a biological or chemical attack.

A convicted terrorist collaborator testified just two months ago about another potential threat, saying in court that he trained for a chemical attack at a camp inside Afghanistan where poison was unleashed to kill dogs.

"In regard to targets in general ... we were speaking about America," Ahmed Ressam testified in July. Ressam said terrorist trainers discussed dispensing poison through the air intake vents of buildings to ensure the maximum amount of casualties.

In the probe of the Sept. 11 attacks, the FBI is investigating whether some of the hijackers who destroyed the World Trade Center practised their approaches by renting small planes at New Jersey flight schools and flying along the Hudson River toward the twin towers.

In other developments:

-- The FBI released a Saudi doctor living in Texas who had been taken into custody and brought to New York for questioning earlier in the investigation. Al-Badr Al-Hazmi, a radiologist whose name was similar to two of the 19 hijackers, returned to San Antonio after nearly two weeks in custody as a material witness -- someone believed to have important information about the investigation.

A law enforcement source, who spoke only on condition of anonymity, said authorities questioned the doctor about whether his credit card may have been stolen by the hijackers or their associates.

-- A Saudi man arrested 20 kilometres south of Washington Dulles International Airport the night after the terrorist attacks passed an FBI-administered polygraph test and faces only an immigration-related charge, his lawyer said. Drew Hutcheson said Khalid al-Draibi was cleared by the FBI after being asked whether he had any involvement in the attacks or whether he knew anything about them in advance.

-- Three men in San Diego who authorities believe knew some of the suspects in the Sept. 11 attacks have been detained as material witnesses and could be sent to testify before a grand jury in New York, a law enforcement official said.

-- In Arkansas, one of five people stopped for speeding has a name that is on the FBI's list of people it wants to talk to in the investigation, said Cross County Sheriff Ronnie Baldwin. All five were detained at the FBI's request.

-- In Spain, police detained six Algerians allegedly linked to Osama bin Laden and to a group suspected of planning attacks on U.S. targets in Europe.

-- In Britain, authorities captured a suspect believed involved in a plot to attack U.S. interests. Also, a woman who was one of three people held in connection with the terrorist attacks on the World Trade Center was released from police custody without charge Tuesday.

-- In France, all seven suspects held for allegedly plotting to attack U.S. targets in Europe have been placed under formal investigation, a step before being charged.