JAKARTA, Indonesia — The top U.S. health official criticized Indonesia's refusal to share bird flu virus samples with the World Health Organization, saying its government was undermining nearly 60 years of global cooperation that led to the production of lifesaving vaccines.

U.S. Health and Human Services Secretary Mike Leavitt, making a two-day stopover that included meetings with Indonesia's president and health minister, acknowledged Monday that improvements to the global body's virus-sharing system could be made.

"But linking it to the sharing of viruses is not something we can support," he said, adding that once "people begin to trade viruses for value ... there will be no end" to it.

Poor countries are obliged to send influenza virus samples unconditionally to WHO, which then makes them available to pharmaceutical companies to use in vaccine production.

That system has made it possible for laboratories to make sure viruses are not "mutating into a form that could become a person-to-person communicated disease," Leavitt said, noting that almost every country in the world has collaborated effectively for 56 years.

But Indonesian Health Minister Siti Fadilah Supari argued the system is unfair and should be changed. She said any vaccine produced from her country's bird flu specimens would be out of reach for its own citizens in the event of a pandemic — too expensive and controlled by wealthy nations.

Supari, who has withheld almost all virus samples from WHO since January 2007, has been especially critical of the United States, one of the system's main backers. She wants developing countries that hand over samples to retain the rights for any vaccines produced from them.

"I'm still pushing for a Material Transfer Agreement," Supari said after talks with Leavitt, adding some progress has been made in recent talks with the U.S. and WHO. She did not elaborate, however. "We don't have any objection (to sharing samples), but it has to have an MTA, with certain conditions."

Indonesia is the nation hardest hit by bird flu, with its 107 human deaths accounting for nearly half the recorded fatalities worldwide.

So far, most human cases have been linked to contact with infected birds. But health experts worry the virus could mutate into a form that passes easily among humans, sparking a pandemic that could kill millions worldwide.

Indonesia is considered a hotspot for that to happen, because of its high density of people and backyard chickens.