KOLKATA, India, Jan 13 (Reuters) - Preliminary results of tests taken after thousands of backyard poultry died in eastern India over the past 10 days showed they were infected with bird flu, but it was unclear if it was the H5N1 virus, officials said.

More than 10,000 birds died in Margram village of Birbhum district in West Bengal state.

"The preliminary tests showed the birds have died from bird flu, but we still don't know whether it is the deadly H5N1 strain," Sunil Kumar Bhowmik, chief medical officer of Birbhum, told Reuters.

"We will quarantine people if we find anybody sick and intensify culling tomorrow morning until we get the confirmation in a few days," Bhowmik said.

Thousands of birds in India were culled in 2006 following three separate outbreaks of the deadly H5N1 virus in the western state of Maharastra.

Neighbouring Bangladesh is still reeling under bird flu with around 21 of the country's 64 districts affected by the deadly virus.

Experts fear the H5N1 virus might mutate or combine with the highly contagious seasonal influenza virus and spark a pandemic that could kill millions of people.

Bird flu has killed more than 210 people in 12 countries since 2003, the World Health Organisation says. (Reporting by Bappa Majumdar)

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