(Adds more infections)

DHAKA, Jan 17 (Reuters) - Health and veterinary workers in Bangladesh have culled nearly 25,000 fowls after bird flu was confirmed at three poultry farms in the country, officials said on Thursday.

Bird flu has spread to the southern coastal district of Borguna and the northwestern Rajshahi district, a livestock ministry official said. Another infection was reported in Jessore, 275 km (170 miles) from the capital Dhaka.

"After the confirmation of bird flu, authorities have begun culling at the affected farms and surrounding areas," the official said. "So far nearly 25,000 chickens, ducks and pigeons have been culled in three districts."

Fowl were also culled in the southern coastal district of Barisal after detection of the H5N1 avian influenza virus.

Suspected outbreaks were also reported at a farm in northern Rangpur district, where the virus has been confirmed in fowl previously.

The H5N1 virus was first reported near the capital in March last year and has since spread to 25 of Bangladesh's 64 districts, forcing authorities to kill more than 300,000 chickens.

So far there have been no cases of human infection in the densely populated country, government officials say.

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

There have been 217 human deaths globally from the H5N1 strain and 350 confirmed cases of infection since 2003, World Health Organisation figures show.

In neighbouring India, veterinary workers began killing thousands of chickens in West Bengal state on Wednesday following what the WHO said was the worst outbreak of bird flu in the country.

Officials said it could take up to a week to cull about 350,000 birds in three districts of West Bengal.

(Reporting by Ruma Paul; Editing by Jeremy Laurence)

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