DHAKA, Dec 31 (Reuters) - Bangladesh culled more than 2,500 chickens after the H5N1 bird flu virus infected more farms in the northern part of the country, officials said on Monday.

The latest infection was detected in two villages in Gaibandha district, about 350 km (210 miles) from the capital Dhaka, an official at the government's livestock department said.

Bird flu was first detected near the capital in March and has since spread mainly to northern districts and forced authorities to cull around 278,000 chickens.

About 4 million Bangladeshis are directly or indirectly associated with poultry farming, but so far there have been no cases of human infection, government and health officials say.

But experts fear the bird flu virus might mutate or combine with the highly contagious seasonal influenza virus and spark a deadly pandemic which could kill millions of people.

Bird flu has killed 213 people in 12 countries since 2003, the World Health Organisation says.

(Reporting by Ruma Paul)

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