ROSTOV-ON-DON, Russia — Authorities say they have culled more than half a million domestic birds on a farm in southern Russia hit by the H5N1 strain of bird flu.

They say more than 600,000 chickens on the Gulyai-Borisovskaya farm in the Rostov-on-Don region have been destroyed to prevent the virus from spreading.

A spokesman for the regional branch of Russia's Emergency Situations Ministry said the virus also sickened birds in the neighbouring Tselinsky district.

In September, authorities reported an H5N1 outbreak at a poultry farm in the neighbouring Krasnodar region, and early in the year the strain was confirmed in several other regions across Russia.

No human cases of bird flu have been reported in Russia, which had its first reported cases of H5N1 in Siberia in 2005.