Washington ? Every Customs inspector will be equipped by January with a pocket-sized radiation detector, but “there are no guarantees” that increased border security will stop a terrorist from smuggling in a nuclear weapon, the Customs commissioner said Wednesday.

Fears of a terrorist nuclear assault on the United States have risen since the Sept. 11 jetliner attacks in New York and Washington.

Customs Commissioner Robert Bonner said in an interview with The Associated Press he knows of no terrorist group trying to smuggle a nuclear device into the country.

“The question is, ‘Should we be concerned about it?”‘ he said. “This is one of those areas where I don’t want to wait and see what happens.”

Since Sept. 11, the Customs Service, the nation’s oldest law enforcement agency, founded in 1789, has shifted its primary mission from detecting smuggled narcotics to stopping terrorists, possibly with nuclear, chemical or biological weapons, from getting into the country.

Specifically, Customs has increased security and provided better training for its inspectors and agents at seaports, airports and border crossings on land. Customs oversees roughly 300 points of entry into the United States.

The agency also is working with other countries to screen cargo containers before their shipment into the United States. Under a recent agreement with Canada, U.S. Customs has put inspectors in Montreal, Halifax and Vancouver to prescreen cargo headed for the United States. Canadian Customs officials have inspectors at some U.S. seaports.

With roughly 6 million cargo containers entering U.S. seaports each year, Bonner said it is critically important to ensure that terrorists don’t use them to smuggle themselves or their weapons into this country.

Still, “there are no guarantees,” Bonner said in the interview. “No system is foolproof.”

About half of Customs’ inspectors 4,000 of them are now equipped with pocket-sized radiation detecters. By January, the other 4,500 Customs inspectors will get the devices, Bonner said.

Customs also is looking to use more sophisticated scanning and detection technology at seaports and land crossings.

Even with the shift in its mission, fighting terrorism isn’t new to Customs. The agency was credited with thwarting a terrorist attack before the millennium celebration.

Customs inspectors stopped an Algerian man at the border at Port Angeles, Wash., in December 1999 and found more than 100 pounds of explosives in the trunk of his car. The man had trained in terror camps run by bin Laden.