Russian officials say they are destroying thousands of domestic birds in an effort to contain the spread of a bird flu outbreak that began in Siberia and has spread west to the Ural mountains region.

Health officials and the Emergency Situations Ministry say the outbreak of the highly potent H5N1 strain of virus could pose a threat to humans.

They also say it could spread to the Mediterranean area and the Middle East as birds migrate westward to avoid the harsh Russian winter.

Officials say the illness, which can be fatal, has not yet spread to humans in Russia. At least 60 people in southeast Asia have died from bird flu since 2003.

On Monday, authorities said the virus had been discovered in the Chelyabinsk region, but it is not clear whether it was the H5N1 strain.