A mutant strain of the deadly bird flu H5N1 virus detected in Vietnam does not appear to pose an increased risk to human health, the United Nations said on Monday.

The UN Food and Agriculture Organisation (FAO) last week voiced concern about the appearance in Vietnam and China of the strain, warning of "a possible major resurgence" of the virus, which developed into a pandemic in 2009.

After Indonesia, Vietnam has recorded the highest number of human deaths from bird flu, with 59 since 2003, according to World Health Organisation (WHO) data.

"The last human H5N1 cases in Vietnam were reported in April 2010, but none caused by the new strain," the WHO and FAO said in a joint statement issued in response to questions from AFP.

"There is no evidence to suggest yet that this new virus strain will have any increased risk to human health."

Bird flu is currently affecting poultry in four provinces, according to Vietnam's animal health department.

The mutant strain, known as H5N1 - 2.3.2.1, was first noticed in Vietnam in 2009. It has replaced the previously dominant strain and has been identified in 16 Vietnamese provinces this year, the UN statement said.

In two of the 16 -- where a further variant of the mutant strain was found -- the current vaccine was only partially effective but outbreaks of the disease were quickly controlled, the UN said.

"Nevertheless, poultry producers and the general public should always take simple precautions to reduce exposure to the virus from infected poultry," it said.

"These include extra vigilance for unusual poultry mortality, rapid reporting of disease to the authorities and good hygiene practices while handling, slaughtering and preparing poultry for consumption."

Despite Vietnam's efforts to control H5N1 since it was first detected in 2003, the virus remains "endemic" with several provinces infected annually, the UN said.

To reduce the threat of infections, changes must be made to the way farmers, traders and markets and slaughterhouses operate, it added.

"There is urgent need for adopting good poultry production practices, particularly in the small farming sector."

The H5N1 virus typically spreads from birds to humans via direct contact.