Croatian authorities examined 13 swans found dead over the weekend near a national park where six other swans tested positive for bird flu, according to the Agriculture Ministry.
Meanwhile, about 10,000 domestic poultry have been killed and incinerated near the park in eastern Croatia where the six infected swans were found Friday. In some cases, police shot poultry after farmers set them free in protest.
The European Commission is preparing a ban on poultry import from Croatia, a move experts say will cause local firms to lose €630,000 a month.
The slaughtered poultry has already caused losses of some €135,000, the government has pledged to compensate farmers this week. Local poultry sales have decreased by up to 50 percent.
On Friday, authorities detected the H5 virus in six swans found dead at the national park in Zdenci. Samples were sent to a special laboratory in Britain to establish whether they had the deadly H5N1 strain, which has devastated poultry stocks across Asia and killed 60 people in the past two years.
The 13 other swans found dead over the weekend in the Nasice pond near Zdenci were being tested by Croatian experts and the results could be known later Monday, Agriculture Ministry spokesman Mladen Pavic told.
The 20-kilometer (13-mile) area around the Zdenci park was disinfected over the weekend and it remains under quarantine.
The H5N1 strain has recently been found in birds in Russia, Turkey and Romania. It is easily transmitted between birds, but is hard for humans to contract, the AP reports.