WARSAW, Poland (AP) — Authorities in eastern Poland say bird flu is responsible for the deaths of at least 25,000 turkeys in poultry farms near the country’s borders with Ukraine and Belarus.

Polish veterinary authorities on Thursday were planning to cull tens of thousands of birds in the Lubartow area, a major poultry farming region. Police were blocking access to the affected area to non-residents.

The chief veterinarian for Lublin province, Pawel Piotrowski, confirmed that the deadly H5N8 virus was responsible for the turkey deaths in two farms in the village of Stary Uscimow, which lies 45 kilometers (28 miles) from the borders with Ukraine and Belarus.

It was not clear how the bird flu virus found its way to the farms.