Myanmar has slaughtered more than 1,000 chickens after discovering another outbreak of the deadly H5N1 strain of bird flu in Yangon, a livestock department official said Tuesday.

The discovery of avian influenza on a chicken farm in the north of military-run Myanmar´s biggest city is the fifth such outbreak this year, leaving officials worried about the rapid spread of the virus.

"More than 1,000 chickens were killed from Saturday to Monday, and we suspect the H5N1 virus is spreading," a senior official of the Livestock Breeding and Veterinary Department said.

"The farm has about 20,000 chickens... it´s a big farm," the official told AFP on the condition of anonymity as he did not have official permission to speak to the media.

The outbreak occurred in Hmawbi township, about 20 miles (35 kilometres) north of the centre of Yangon. Myanmar previously confirmed four outbreaks of the H5N1 virus this month in suburbs of the city.

Authorities have not revealed the total number of birds killed since this year´s first outbreak.

A total of 168 people worldwide have died of bird flu since 2003, mostly in Asia, World Health Organisation figures show.

No human cases have been found in Myanmar, but health ministry officials said they were monitoring those who may have been exposed.

"About 960 people who had contact with fowls, as well as their family members around the outbreak areas, are still under surveillance," Kyaw Nyit Sein, deputy director general of health ministry, told AFP on Tuesday.

"There is no positive case yet among them."

Myanmar had declared itself bird-flu free in September after months without any new cases of the disease following an outbreak around the central city of Mandalay in March 2006.

The UN´s agricultural agency has praised Myanmar´s normally secretive government for being "quick and effective" in its response to new outbreaks, and is providing 1.4 million dollars in assistance to help fight the disease.