Tests are continuing to try to establish the source of the outbreak of the deadly H5N1 strain of bird flu discovered on a British farm.
UK government officials confirmed that the virus found in birds on the free-range turkey farm in Redgrave, Suffolk was the potentially deadly version of the disease.
Authorities are now focusing on how the strain came to be back on British shores ten months on from the last outbreak.
Fred Landeg, acting chief veterinary officer, said the disease in the latest outbreak is closely related to one found in birds in the Czech Republic and Germany in the summer.
The discovery suggests the virus could have been spread to the UK by wild birds, but animal health experts are investigating all the possibilities.
A cull of 5,000 turkeys, more than 1,000 ducks and 500 geese on the infected rearing site at Redgrave Park farm is likely to carry on today, according to the Department for Environment, Food and Rural Affairs.
The cull began yesterday after the alarm was raised on Sunday by poultry producer Gressingham Foods, based in Woodbridge, Suffolk, following turkey deaths at the farm.
Protection and surveillance zones, set at 3km and 10km respectively, and a wider restricted area covering the whole of Suffolk and much of Norfolk have been put in place.
They restrict the movement of birds and require them to be housed and isolated from wild birds.
A report by Defra into the last outbreak of H5N1 at the Bernard Matthews poultry plant in Holton, Suffolk, in February also initially blamed wild birds.
But it was later decided the most likely source of the infection was imported turkey meat from Hungary.
