The Food and Drug Administration (search) isn't ruling out legal action if cities or states defy its ban on importing cheaper drugs from Canada, Commissioner Mark McClellan said Friday.

In an interview with The Associated Press, McClellan said the FDA has successfully dissuaded many states from starting such programs by arguing that there are better ways -- such as buying generic -- to bring down the costs of prescription drugs.

"Our first preference is to try to work directly with the cities and states," McClellan stressed.

But when pressed, he added, "I'm definitely not ruling out legal action if necessary to assure safety."

Americans have long flocked to Canada to fill prescriptions that, for brand-name drugs, can cost less than half the U.S. price, thanks to Canadian price controls.

But what began as patients crossing the border to buy their own drugs has turned in the past year into a booming Internet and mail-order industry that supplies Americans who never leave home.

Two cities -- Springfield, Mass., and Montgomery, Ala. -- are the only governments buying drugs from Canada so far. But states from New Hampshire to Wisconsin are studying the issue or say they're close to starting their own programs.

Importing medicines (search) from abroad for resale in the United States is illegal, and the FDA says it cannot guarantee the drugs' safety -- or even that the drugs come from Canada instead of originating in poorer countries like Thailand.

So far, the FDA has targeted suppliers, winning a court's backing in shutting down one company, Rx Depot Inc. (search) Another major supplier shut its U.S. offices and moved to Canada.