LONDON (AFP) - Veterinary authorities confirmed on Tuesday an outbreak of the potentially lethal Asian strain of bird flu in eastern England, in a new blow to the British farming industry.

More than 6,000 poultry were ordered to be slaughtered at the site near Diss in Norfolk, where an exclusion zone was imposed on Monday after a suspected outbreak was found.

"I can now confirm that the strain of avian influenza found in the infected premises is the highly pathogenic avian influenza H5N1 strain," said deputy chief veterinary officer Fred Landeg.

"It is of the Asian lineage. It is closely related to strains of the highly pathogenic avian influenza found this summer in the Czech Republic and in Germany," he added.

On Monday, British officials ordered the slaughter of some thousands of poultry at the farm, which houses turkeys, ducks and geese, near Diss in Suffolk, eastern England.

The cull involves some 5,000 turkeys, more than 1,000 ducks and 500 geese.

They also announced a three-kilometre (1.8-mile) radius protection zone and a 10-kilometre surveillance zone were imposed around the farm in the county of Suffolk, where there was an outbreak of H5N1 in February.

Authorities have also announced further restrictions in a wider area as a "precautionary measure."

Landeg said the operation to contain the latest outbreak would be tough. "This will not be a quick exercise. This is a particularly challenging site," he said.

Probes into the source of the virus are focusing on wild bird transmission, he said, but stressed they were keeping an "open mind" about the exact source.

The new bird flu cases are the latest blow to hit the British farming industry, after an outbreak of foot and mouth disease over the summer centred on a government laboratory in Surrey, south of London.

In the February outbreak some 159,000 turkeys were killed as a precaution at a plant near Holton in Suffolk after an outbreak, which led some countries to impose import bans on British poultry.

An official report into the outbreak at the Bernard Matthews poultry plant later said it was most likely the H5N1 infection reached the flock via imported turkey meat from Hungary.

The H5N1 strain first emerged in Asia in 2003, and has caused some 205 deaths in humans, with Indonesia and Vietnam among the worst hit countries, according to World Health Organization figures.

Scientists fear that H5N1 will eventually mutate into a form that is much more easily transmissible between humans, triggering a global pandemic.

The original source is thought to have been wild migratory birds.

H5N1 has mainly affected Asia and some parts of Africa, but the Food and Agricultural Organisation warned last month that the virus could be transmitted to poultry in Europe by ducks and domestic geese seemingly in good health.

Besides Indonesia, deaths have been recorded in Azerbaijan, Cambodia, China, Egypt, Iraq, Laos, Nigeria, Thailand, Turkey and Vietnam.