Russia's veterinarian authorities confirmed Tuesday that some 250 swans had died of bird flu in the southern region of Astrakhan in the past week.

"Tests showed that nearly 250 swans had died of bird flu" in the Volga River delta in southern Russia, Yevgeny Nepoklonov, deputy head of the Federal Veterinarian and Phytosanitary Control Service, told the Itar-Tass news agency.

"Villages in the Volga delta are under quarantine, and domestic birds are staying indoors," Nepoklonov said.

The Astrakhan veterinarian service said swan deaths started near the Astrakhan Nature Park a week ago. The region's chief veterinarian, Alexander Vasilyev, said many birds had gathered in the Volga River delta but only swans born in spring died.

"They might have been weakened by the long voyage," he said.

The Agriculture Ministry said four other regions are still affected by the bird flu -- Altai, Kurgan, Chelyabinsk and Tambov regions -- but quarantine is expected to be lifted in previously infected localities in the Altai, Tambov and Chelyabinsk regions later this week.

The bird flu virus, strains of which can spread to humans and can be fatal, has claimed the lives of more than 60 people in Southeast Asia since 2003.