Ten Middle Eastern men have been arrested by US authorities on suspicion of fraudulently obtaining licences to transport hazardous materials.
Yesterday's arrests in Missouri, Michigan and Washington state followed FBI warnings the next terrorist strikes may be with chemical or biological weapons.
Authorities said as many as 20 people who had the bogus permits, some of whom may have connections to the 19 hijackers in the September 11th attacks, have been charged but may not be linked to the attacks.
FBI affidavits for the 10 arrested said 18 people from seven states had falsely obtained licences in Pennsylvania to haul hazardous materials between July 1999 and February 2000.
It was too early to tell whether any of those arrested are connected to the attacks on the World Trade Center and the Pentagon, said a Justice Department spokeswoman.
Those arrested got the licences from Pennsylvania state, where a drivers' licence examiner in Pittsburgh provided permits to people who did not take required tests, had suspended licences or were otherwise not eligible, according to court records.
AP