Indonesia has reported its first human deaths attributed to bird flu. Health officials still do not know how the victims contracted the virus.

The Indonesian Health Ministry says tests in Hong Kong indicate a father and his two daughters died earlier this month in Jakarta from the virulent H5N1 bird flu virus.

Health minister Siti Fadillah Supari said test results on the father led her to conclude that all three died of bird flu.

But the World Health Organization's representative in Indonesia, Georg Peterson, said only the father tested positive for the virus. "What we know so far is that three people of the same family died of influenza-like illnesses and that they confirmed H5N1 is the father in the family. We do not yet know what the exposure could be or the source of infection could be," he said.

Mr. Peterson said there is no evidence yet any of the three had contact with infected poultry, but signs do not point to human-to-human transmission. "What is happening is all contact with these people are being monitored closely for fever and influenza symptoms and if no one is getting sick in the next few days it's most likely that there's no human-to-human transmission here," he said.

Millions of chickens have been slaughtered since the H5N1 bird flu virus first started infecting poultry populations across Asia in late 2003.

Dozens of people have died from the virus in Thailand, Vietnam and Cambodia, with health experts saying most of those who died caught bird flu from contact with infected poultry.

But the WHO has warned the virus may mutate into a form more easily transmitted between humans.