-- Russian officials have quarantined a large poultry farm in Siberia because of a suspected outbreak of bird flu, news reports said Saturday. If confirmed, it would be the first major occurrence of the lethal virus among birds in Russia, and international health officials expressed concern that the disease had spread closer to Western Europe.

About 142,000 birds are being monitored at a commercial farm in the Omsk region of Siberia, 1,400 miles east of Moscow, the Russian news agency Interfax reported, quoting a federal agency that tracks the disease. The presence of the deadly H5N1 strain of avian influenza was reported last month in Siberia, but only among wild birds and free-range chickens on small family farms.

Avian influenza has killed at least 61 people in Vietnam, Thailand and Cambodia since early last year, mostly farmers and poultry workers in close contact with the animals. Millions of birds have been slaughtered in Asia in an attempt to control the disease.

The World Health Organization has warned that the viral strain affecting chickens, ducks and wild fowl could develop into a form that spreads easily among humans, exposing millions of people to the disease. The exact means of transmission is unclear, and it is not conclusively known whether the disease can be contracted from eating infected poultry.

WHO reported Thursday that the spread of the H5N1 strain in Russia "is of concern because it creates further opportunities for human exposure."

Russian officials said there have been no human infections since the virus was detected last month.

The federal consumers' rights and welfare agency said in a statement that it had "mapped out and passed on to the regions a package of sanitary and anti-epidemic measures" to prevent bird flu deaths.

Russia has also stepped up health inspections of chickens and other birds in the past month.

There are about 233 million head of poultry in commercial enterprises in Russia, according to the Russian Poultry Union. The spread of the disease into the industry would be economically devastating for the country and could affect neighboring countries, including those of the European Union.

International officials fear that, in September, migrating birds escaping the Russian winter might carry avian influenza across the Black Sea and into southeastern Europe and North Africa. Countries in the region and in the European Union have begun banning the importation of feathers and live birds from Russia.

"We are preparing for a worst-case scenario," said Renate Kunast, Germany's consumer protection minister, announcing emergency restrictions this month on poultry kept in the open. Free-range chicken is popular in Germany.

The Netherlands had already ordered poultry farmers to move their operations indoors to reduce the risk of exposure to wild birds and to help contain any outbreak. The British government is sending doctors 50-page pamphlets with information on dealing with a human outbreak, the Financial Times reported.

WHO, meanwhile, is negotiating with the Swiss pharmaceutical firm Roche for a donation of 3 million doses of Tamiflu, an antiviral drug effective against bird flu. WHO and other health organizations have expressed concern that the global capacity to manufacture vaccines in the event of a pandemic might be insufficient.

Russian officials said that if the presence of bird flu were confirmed at the Omsk farm, all the poultry there would be killed, according to Interfax.

About 11,000 birds have died of the disease in Russia, and an additional 127,000 have been slaughtered on small farms, officials said. Up to 40 Russian villages have been hit by bird flu, and 78 are under watch, according to the federal veterinarian and plant health oversight service. But some of the measures introduced in the European Union, such as moving poultry indoors, are difficult to impose on Russia's small family plots.

As recently as Thursday, the Russian poultry industry, in an effort to reassure consumers, was stressing that the outbreak had not affected any birds on commercial farms.

"All measures were taken in advance so that bird flu would not affect our enterprises, and the situation is being permanently monitored," Vyacheslav Lukyanov, deputy general director of the Russian Poultry Union, told Interfax.

A team from the U.N. Food and Agricultural Organization was expected to visit Russia soon to advise officials on combating the outbreak.

A chicken is removed Friday at a small farm affected by bird flu in a Siberian village. The first suspected outbreak on a large farm was reported Saturday.