BANGKOK - Thailand has suffered its first outbreak of the H5N1 bird flu virus in six months, an Agriculture Ministry official said on Monday after a rash of outbreaks in Vietnam and four human deaths in Indonesia this year.

"The lab results confirmed that some ducks in the northern province of Phitsanulok have been infected with H5N1 bird flu virus," Livestock Department chief Pirom Srichan told Reuters.

"We have culled about 1,900 ducks in the area."

Thailand's last outbreak of the virus in poultry was in late July, and the last human death in August, the country's 17th since the virus re-emerged in Asia in late 2003.

The World Health Organization says the virus has killed 159 people worldwide since 2003 by January 12, including 61 in Indonesia.

It has urged countries to be vigilant because H5N1 continues to circulate in poultry.

Vietnam, which has had no human H5N1 cases since November 2005, is battling new outbreaks in poultry in the Mekong Delta.

Scientists fear the virus could mutate into a form that jumps easily between people although it has not yet shown an ability to do so.