JAKARTA (AFP) - A fourth person has died in Indonesia from bird flu, the World Health Organisation and the health ministry said, as a scientist accused the government of covering up the initial outbreak.

Health ministry official Renuizar Rusin confirmed the country now has four bird flu fatalities. Another ministry official, Hariyadi Wibisono, said the latest victim was a 23-year-old man who died on September 30 in Bogor, south of Jakarta.

Results received Monday from tests conducted in Hong Kong confirmed the cause of death, he said. The WHO raised Indonesia's human death toll from bird flu to four on its website.

Wibisono said samples taken from people who had contact with the deceased had been analyzed and returned negative.

Chairul Nidom, an Indonesian microbiologist who first revealed the bird flu outbreak, said the government covered up the outbreak among poultry for about six months and tried to halt it secretly using dubious vaccines imported from China.

Only a day after Nidom announced the outbreak in January last year the government confirmed it, said Nidom, a researcher at the Center for Tropical Diseases at Airlangga University in Surabaya.

"The government has in the past often been tardy in anticipating outbreaks and it seems that old habits die hard. Little has changed," he said.

"If action had been taken promptly, the damage wouldn't have been great and the risks to humans could have been minimized," Nidom said.

The deadly H5N1 strain of the virus has killed at least 60 people in Asia since late 2003, most of them in Vietnam.

WHO country director in Indonesia, Georg Petersen, said the country's latest bird flu victim had a history of contact with birds. "As far as we know this H5N1 is circulating in birds in Indonesia.

As long as that happens we expect there will be occasional infections in humans. It doesn't mean the situation has changed," Petersen told AFP. "It means we have to continue good surveillance both in humans and in animals," he said.

Scientists fear the current H5N1 strain of the virus may mutate, acquiring genes from the human influenza virus that would make it highly infectious as well as lethal -- possibly killing millions worldwide like a pandemic in 1918.

Nidom said he suspects there have been cases of human-to-human transmission in the country.

"There have been cluster cases," he said. "My hypothesis is that the incidence rate is linked to genetics, whether its through blood cells I'm not sure, but people who are not related to the sufferers, including the spouse, are less likely to be affected," he added.

Scientists believe there may have been cases of limited human to human transmission involving people in close daily contact. But even if one of these close contact cases were clinically proved to be human-to-human transmission, the WHO says it would not raise the risk of a pandemic.

The United Nations Food and Agriculture Organization (FAO) said Monday it would send a team of experts to Indonesia to help the country combat the deadly virus at source, by organising a house-by-house search for infected birds on the island of Java.