PESHAWAR, Pakistan (AFP) - Pakistani authorities reported a new outbreak of avian flu at a commercial poultry farm in the country's northwest, killing thousands of birds, officials said.

Tests conducted at a government-run laboratory in Islamabad confirmed the presence of the deadly H5N1 strain of bird flu at a farm in Swabi district, local livestock department chief Ibrahim Khan told AFP.

"The virus was detected after the owner of the farm informed us on Friday that some 4,000 birds had died within the past few days," he said.

"We got the confirmation on Saturday, sealed the farm and culled around 2,000 birds," he said.

All workers on the affected farm were examined by the ministry of health but none was found to have been affected by the virus, he added.

Local health officials are monitoring surrounding farms and advised them to take precautionary measures including vaccination of birds, he said.

Pakistan's first H5N1 cases were detected in March 2006 at two chicken farms in North West Frontier Province, prompting consumer panic and a mass slaughter of birds at several sites.

The virus resurfaced in early February last year among chickens in Rawalpindi, adjoining Islamabad, and in peacocks in the northwestern city of Mansehra.

In February this year Pakistani officials sealed off several farms and culled around 10,000 chickens after an outbreak in the southern port city of Karachi.