ASTANA (Reuters) - A deadly strain of avian influenza that can infect humans has spread to three more Kazakh villages, a senior official at the Central Asian state's Agriculture Ministry told Reuters on Thursday.

The disclosure comes a day after Kazakh officials said the strain, H5N1, was detected in a village in the northern Pavlodar region that borders Russia, which has also reported a bird flu outbreak that continues to spread.

The H5N1 strain has killed more than 50 people in Asia since August 2003. Although no humans have yet been affected in Kazakhstan or Russia, there are fears the disease might now spread to humans on the Eurasian landmass.

Talgat Abulgazin, the head of the ministry's veterinary disease monitoring department, said he believed the virus's spread among poultry in Kazakhstan could be checked.

``The epizootic situation for this disease is under control,'' he said in an interview, using the term for an outbreak of disease affecting many animals of the same kind at one time.

``(But) I cannot guarantee that we will be able to eradicate this in Kazakhstan, although all efforts are being made to do so.''

Tests had shown that H5N1 was now present in three other villages outside the Pavlodar region: two in the Akmolinsk region to the west, and one in Karaganda region, in central Kazakhstan, Abulgazin said.

``If all our agencies work together under one single command, we may be able to do something. I think we may be able to stop the spread of this disease,'' Abulgazin said.

There are concerns that migrating birds could spread the disease further to Europe and eventually the United States.

Reflecting fears that bird flu's jump to humans could unleash a global pandemic, a dozen Asian nations on Thursday agreed to build a regional stockpile of anti-bird flu drugs.

MIGRATION THREAT

Abulgazin said there was an immediate threat to Kazakhstan from infected birds in Russia, to the north.

``We are of course worried about the moment when the migration of birds from the north starts,'' Abulgazin said. ``The birds will have to makes stops on our territory and that's something to be concerned about.''

The migration is expected to start in September.

Kazakhstan's sheer size and small population -- 15 million people in a country the size of Western Europe -- has led Kazakh officials, who are culling birds in affected areas, to strike a calm note about the outbreak.

The affected areas are under quarantine and birds inside them are being culled.

But the disease also continued to advance through Russian Siberia on Thursday, with mass deaths of wildfowl and poultry registered in three more villages there -- in the Kurgan and Altai regions near the Kazakh border, media reported.

But there was no official word on whether the virus found in those regions was the deadly strain that can kill humans.

Mikhail Kozlov, Altai's acting governor, was quoted as saying by Itar-Tass news agency that the situation in the steppe region remained ``alarming.''

``It is necessary to take most decisive measures to prevent the disease from spreading in the region and maintain people's safety,'' he told Tass in the Altai capital of Barnaul.

The Russian Emergencies Ministry said in a statement the number of bird deaths rose to 10,170 on Thursday -- up from just over 8,300 on Wednesday. The ministry said most deaths occurred in the Novosibirsk, Tyumen, Kurgan and Altai regions of Siberia.