Tokyo ? Authorities have detected another outbreak of bird flu at a poultry farm near Tokyo, the Agriculture Ministry said Monday.

Officials have extracted and identified a virus in the H5 family from chickens at a poultry farm in Ibaraki state, the ministry said in a statement.

All birds at the farm will be culled except for those kept in enclosed poultry houses that were unaffected, the ministry said. Kyodo News agency said about 260,000 chickens would be culled.

The strain involved is less virulent that the H5N1 variety that has ravaged poultry and killed more than 60 people in Southeast Asia since 2003.

Chickens at two other farms in Ibaraki were also tested and found to be carrying antibodies for the virus, meaning they were infected in the past but had survived.

Birds at those farms would not be culled unless the virus is actually detected among them. Instead, authorities would step up monitoring of those farms, the ministry said.