Indonesia will not share bird flu samples with the World Health Organization without a legally binding agreement promising the virus won't be used to develop an expensive commercial vaccine, the health minister said Wednesday.

Siti Fadilah Supari, digging her heels in following a weekslong standoff with the global body, said a letter of guarantee from WHO's director general Margaret Chan late last month was not good enough.

"That's just an agreement in principle ... we need one that is legally binding," she told reporters, adding that Asia Pacific health leaders meeting in Jakarta later this month will seek a change in the WHO's 50-year-old virus-sharing system.

The system, which enables influenza samples to be freely passed throughout the global community for public health purposes, needs to be revised so it is "fair for developing countries, poor countries, affected countries," Supari said.

"We will not share our virus sample, without a change in the rules," Supari said.

Several countries are developing vaccines to protect against H5N1, the bird flu virus strain blamed for 168 human deaths worldwide — more than a third of them in Indonesia.

The virus remains mainly an animal disease, but experts fear it may mutate into a form that easily spreads between humans, potentially killing millions.

Indonesia is worried that large drug companies will use its H5N1 strain, sent to WHO affiliated laboratories to confirm human infections, to make vaccines that ultimately will be unaffordable for developing nations.

Chan told Supari in a Feb. 28 letter seen by The Associated Press that WHO would use Indonesia's strain of the virus "for public health risk assessment purposes only."

Until a formal agreement is reached, WHO will obtain authorization from Indonesia before sending any "H5N1 strain as a vaccine seed virus to a vaccine producer for production of influenza H5N1 vaccine," the letter promised.

The government's decision to withhold the vaccine was a major departure from WHO's virus-sharing system, in which influenza samples are freely passed throughout the global community for public health purposes, including vaccine development.

Samlee Plianbangchang, the WHO's Southeast Asia director, said he was confident this month's meeting in Jakarta would go a long way to finding a solution that would satisfy both sides.

"It's a matter of time," he said. "I'm sure that there is a common path, WHO and the country can move together."