Russian authorities say the H5N1 strain of bird flu deadly to humans has been confirmed on at least two farms outside Moscow where the virus was first detected last week.
Emergency situations ministry officials in Moscow Monday, said tests found the strain in two of five districts where 150 birds died between February 10 and 17. Results of tests from the remaining three districts are expected later this week.
A senior official of Russia's federal agricultural oversight agency says the H5N1 strain found on the farms is similar to the most dangerous Asian version subtype.
Russian authorities say a market in southern Moscow is the source of last week's avian influenza outbreak. The origin of the market's birds is not known, but veterinary officials say bioterrorism has not been ruled out.
No human cases of bird flu have been reported in Russia.
Meanwhile, Russia's Interfax news agency says prosecutors Monday opened a criminal investigation into whether any violations of veterinary laws led to the bird flu outbreak.
Bird flu in Russia was first detected in Siberia in 2005, but officials say this is the first time the virus, particularly the H5N1 strain, has been found so close to Moscow, which is home to some 10 million people.
The H5N1 bird flu strain has killed 167 people since 2003, mostly in Asia. Most of the victims had direct contact with the infected birds.
Some information for this report was provided by AFP, AP and Reuters.