The World Health Organization insisted that a strain of bird flu that has killed millions of birds in Indonesia is potentially deadly to humans, contrary to claims by Indonesian officials.

WHO expert Steven Bjorge said an Indonesian agriculture ministry official had been inaccurate by saying that the virus found here was non-lethal type. "There was misinterpretation and we're going to clarify that," Bjorge told AFP.

The agriculture ministry's director for animal health, Tri Satya Naipospos, said this week that preliminary test results from a Hong Kong center with which the WHO collaborates showed the H5N1 bird flu strain found in Indonesia was of a genotype that does not infect humans.

But Bjorge said all the bird flu outbreaks in Asia, which have killed at least 30 people in Vietnam and Thailand this year, were of the same Z genotype.

"It is highly pathogenic to birds. It can also transmit to humans but we have not seen it yet in Indonesia or China," Bjorge said.

"There are sublineages of H5N1 genotype Z. The virus in Indonesia is somewhat different from the virus in Vietnam and Thailand but that does not mean they are not all genotype Z," he said.

Thousands of poultry died in a bird flu outbreak in Indonesia early this year. In July the country launched a major vaccination program to eradicate the virus, which was still lingering in some districts.

Officials said the virus had resurfaced because farmers had neglected procedures to combat it by using illegal vaccines and restocking their poultry too early.

But the WHO says the most important control measures are rapid destruction of all infected or exposed birds, proper disposal of carcasses, and the quarantining and rigorous disinfection of farms.

During this year's outbreak in Indonesia, a senior agriculture ministry official admitted the government had been involved in only one cull. Farmers were destroying stocks on their own initiative, the official said.

The agriculture ministry said 1,510 fowl died of bird flu in several areas of Java island between July and September this year but it said the new outbreak was confined to previously infected areas.

Thai officials last week confirmed the country's first probable case of human-to-human infection of bird flu following the deaths of a mother and daughter.

A variation of bird flu was blamed for the deaths of as many as 40 million people worldwide in 1918.