HANOI (AFP) - Health experts are investigating Vietnam's first suspected human bird flu case in 18 months, a WHO official said Wednesday, as Indonesia confirmed its 77th death and Pakistan reported a fresh outbreak among poultry.

The World Health Organisation is looking into the suspected bird flu case in Vietnam following a series of new outbreaks on poultry farms, a WHO spokeswoman said.

If confirmed it would be the first human infection in one-and-a-half years in Vietnam, one of the countries hardest hit by the virus, with 42 human fatalities between 2003 and November 2005.

In Indonesia, a five-year-old girl is the latest victim of the disease, taking the country's death toll from the virus to 77, a health ministry official said. Indonesia is the country worst hit by the virus.

The girl died last Thursday at a hospital in Solo city on the main island of Java, said the official from the ministry's bird flu information centre.

Speaking about the suspected case in Vietnam, WHO spokeswoman Dida Connor told AFP: "We're working closely with the ministry of health on a suspected H5N1 case.

"The virus has been circulating for a long time in the poultry. If this were to be a human case, it would not be surprising."

Vietnamese state media have reported that an initial test last Sunday on a 30-year-old farmer from northern Vinh Phuc province, now in a critical condition in a Hanoi hospital, had proved positive for bird flu.

The man had helped slaughter chickens for a wedding about one month ago from a neighbouring farm, where several of the flock of 500 birds later died. A Vietnamese veterinary team this week went to assess the farm.

Connor stressed that the WHO was awaiting Vietnamese test results on the case, which would then have to be verified by the UN health body's own laboratory tests.

"We don't yet have an official confirmation of this suspected case, but we are following it closely," health ministry spokesman Nguyen Duc Long said.

Vietnam has reported no new human infections since November 2005 but the virus remains endemic in wild and domestic bird populations.

The Indonesian girl had come in contact with at least 20 dead chickens around her home and in her neighbourhood in Wonogiri town in Central Java, the health ministry's bird flu information centre official said.

"The results of tests showed that she was positively infected with the bird flu virus," said the official, identified as Ningrum.

Another 20 people have been confirmed as infected around the country and are being treated, the official added.

The latest death comes after Indonesia earlier this month resumed sending virus samples to a WHO laboratory in Tokyo, ending a five-month freeze.

In Pakistan, officials have culled thousands of birds after three poultry farms in the suburbs of the Pakistani capital, Islamabad, were hit by bird flu.

"The disease at the three farms killed 6,000 birds and we culled the remaining 5,000 on Tuesday," agriculture and livestock ministry spokesman Mohammad Afzal told AFP.

Afzal said all workers on the affected farms were examined by the ministry of health but "none was found affected by the virus."

Avian influenza is known to have killed 185 people worldwide since late 2003, most of them in Southeast Asia, according to WHO figures.

Scientists fear the virus could mutate into a form easily spread among humans, leading to a global pandemic with the potential to kill millions.

The fear stems from the lessons of past influenza pandemics. One in 1918, just after the end of World War I, killed 20 million people worldwide.