Japanese officials are investigating a possible fresh bird flu outbreak after 23 chickens were found dead at a farm, the country's Agriculture Ministry said Tuesday.

The latest suspected outbreak occurred in Shitomi town in southwestern Miyazaki prefecture (state), which saw two separate bird flu cases earlier this month, Agriculture Ministry official Yasushi Yamaguchi said.

The latest case would mark Japan's fourth bird flu incident in the past month. Authorities tested 13 of the 23 dead birds at the Shitomi farm, and seven of those tested showed initial signs of having a bird flu viral infection, Yamaguchi said.

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"We found the dead birds today and are investigating whether the virus is present," Yamaguchi said. Official results could take days.

The farm was quarantined and chicken ranchers within a 10-kilometer (6-mile) radius were told not to transport poultry out of the area.

Separately Tuesday, officials were trying to determine whether the virus that killed dozens of chickens in the western prefecture of Okayama was of the deadly H5N1 variety.

The H5N1 bird flu virus was pinpointed in the earlier Miyazaki outbreaks, which forced the slaughter of thousands of chickens in the region.

The H5N1 virus has prompted the slaughter of millions of birds across Asia since late 2003, and caused the deaths of at least 163 people worldwide, according to the World Health Organization.

Japan has confirmed only one human H5N1 infection, and no human deaths.

The bird flu virus remains hard for humans to catch, but international experts fear it may mutate into a form that could spread easily among people and possibly kill millions around the world.

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