Bulgaria´s first suspected cases of bird flu in poultry were not caused by the potentially lethal H5 or H7 viruses, final test results from the EU reference laboratory has showed.

Samples of the virus, detected in July on two farms in the village of Slanchogled, near Djebel in southern Bulgaria, "proved negative for the highly pathogenic strains H5 and H7, dangerous for humans," the national veterinary service said in a statement, citing the results from the laboratory in Weybridge, Britain.

The samples were however positive for "Newcastle disease and a low-pathogenic form of bird flu," which are not lethal to humans, it added.

Bulgarian veterinary authorities culled some 1,000 birds in the two affected farms and the country banned all exports to the EU of live poultry, raw poultry products and brood eggs to prevent a spread of the viruses.

The suspected bird flu outbreak was the first in domestic poultry in Bulgaria, although four cases of the potentially deadly H5N1 bird flu virus were registered in February in wild swans in the north of the country.