The United States is sending a stockpile of the antiviral drug Tamiflu to Asia as a first defense against a possible flu pandemic, the U.S. health chief said Monday.

Mike Leavitt, U.S. secretary of health and human services, said Washington has shipped treatment courses of Tamiflu to a secure location in an unnamed Asian country.

The drug, produced by the Swiss-based Roche Holding AG, is regarded as the best initial defense against a pandemic resulting from a possible mutation of the deadly H5N1 bird flu virus into a strain easily passed between people.

"It is a stockpile that would belong to the United States and we would control its deployment," Leavitt told reporters in Geneva, where he was attending the World Health Assembly, the annual meeting of the U.N. health agency's 192 members.

He declined to say how many courses had been sent but said the shipment would arrive later this week.

The courses sent to Asia will be used to support international containment efforts in the event of a human pandemic, but the United States could redirect the stocks for domestic use should it become clear that containment overseas was not feasible.

Leavitt said the U.S. maintained its long-term goal of stockpiling enough Tamiflu to treat 25 percent of the U.S. population as part of its pandemic preparedness plan. He said the U.S. would have 26 million treatment courses by December, and the necessary 75 million by the end of 2007.