Japan will cull 170,000 more chickens after a bird flu virus from the H5 family was detected at farm north of Tokyo, a news report said Tuesday.

The Agricultural Ministry said Monday that chickens at the farm tested positive for antibodies for the virus, though no viruses had been found. But local authorities corrected that announcement Tuesday, saying the virus had been detected in two chicken pens at the farm in Ibaraki prefecture (state), about 64 miles north of Tokyo, public broadcaster NHK reported.

Officials said the chickens probably had the H5N2 strain of the virus, which is less virulent than the H5N1 strain that has ravaged Southeast Asia since 2003 and killed at least 63 people there.

The 170,000 chickens in the two pens will be culled nevertheless, NHK said.

Local authorities were not available for comment Tuesday night.

The virus was detected last Friday at Moriya Farm, but local authorities failed to report their findings because they wanted to prevent panic, NHK quoted Ibaraki official Hitoshi Kashimura as saying.

Agricultural authorities found H5 antibodies at several other farms in Ibaraki last week, prompting them to cull 180,000 free-range chickens. But this was the first time the bird flu virus, rather than antibodies, were detected in Japan since August, NHK said.

Ibaraki prefecture has prohibited the movement of eggs or chickens within a 3.1-mile radius around the farm. The quarantine affects some 1.23 million chickens.

The announcement came as Vietnam, the country worst hit by bird flu, confirmed its 42nd human death from the virus.

The 35-year-old man, who died on Oct. 29, was admitted to a Hanoi hospital four days after his family bought a prepared chicken from a market near his house, a health official said.

Most human cases have been traced to direct contact with sick birds, but health officials fear the H5N1 virus could mutate into a form that is easily passed between humans, possibly setting off a deadly flu pandemic.

The World Health Organization has warned governments to be ready for when — not if — a deadly pandemic arrives that could kill millions and cost the global economy $800 billion in a single year.

In late October, Japan set up a task force to plan against a possible outbreak of bird flu among humans.