Come autumn, migratory birds flying to warmer climes could spread the H5N1 virus to southern Russia and from there to the Mediterranean and Middle East. And in spring next year, bird flu could spread to the entire European part of Russia.

Authorities have already culled more than 11,000 birds, the Emergency Situations Ministry said in a statement, adding that measures were being taken to stop the spread of the virus among domestic fowl and to prevent cases among humans.

But the country's public health chief warned in a letter to regional health officials that the virus -- believed to be transmitted by migratory wild birds -- could reach the Black Sea and Caspian Sea regions this autumn and speed right across European Russia by the spring.

A separate order signed by the official, Gennady Onishchenko, urged regional officials to step up their efforts to contain the bird flu. The disease has swept through poultry populations in Asia since 2003, killing tens of millions of birds and at least 60 people, most of them in Vietnam and Thailand.

Nearly 1,000 Birds Have Been Slaughtered

The Russian government revealed Monday that the H5N1 strain, which can fatally infect humans and which first appeared in western Siberia in July, had spread to the Ural Mountains region of Chelyabinsk. The Ural Mountains divide the European and Asian parts of the country.

A local emergency situations ministry official quoted by the RIA-Novosti news agency said Tuesday that nearly 1,000 birds had been slaughtered in the Oktyabrskoye settlement in Chelyabinsk, where geese, chicken and ducks have caught the flu.

The official added that veterinarians had examined 65 poultry workers and local residents and the district hospital near Oktyabrskoye had prepared an isolated ward in case anyone falls ill with the virus.

Another village in the Chelyabinsk region, Maloye Shumakovo, was quarantined, the Interfax news agency reported. Seventy-nine chickens and 21 ducks have died in three of the 1,400 households there, it said.

No cases of human infection have been found in Russia.

Authorities believe the virus was brought to the country by migratory birds that fly north from Southeast Asia in the spring.

Migratory Birds Could Spread the Virus

In his letter to regional health officials, posted Monday on the Web site of the Russian consumer rights' watchdog, Onishchenko warned that come autumn, migratory birds flying to warmer climes could spread the virus to southern Russia and from there to the Mediterranean and Middle East.

And in spring next year, bird flu could spread "to the entire European part of Russia," he said.

An order by Onishchenko issued on Aug. 11 but made public only late Monday called for accelerated efforts to combat the spread of the outbreak. It said the situation required "additional measures and greater coordination" between federal and regional agencies.

He requested that regional authorities assist veterinary and health officials in preventive measures and "make the necessary changes to the regional preparations against the flu epidemic."

He also asked the Interior Ministry to provide personnel to help quarantine affected areas and instructed the Health Ministry's regional offices to compile lists of people and their families who have come into contact with infected birds.