Confirmation of the strain, which is potentially fatal to humans who come into contact with infected birds, came on Saturday evening at Odintsovo and Domodedovo. Both are within a 50-kilometre (31-mile) radius of the capital.

All the birds at the farms had been killed, said officials.

"We are taking all necessary measures," said Nikolai Vlasov, director of veterinary inspection for agricultural agency Rosselkhoznadzor.

"The farms have been disinfected. The experts are treating vehicles that are leaving the areas where the virus was discovered," said Vlasov, adding that access in and around the region had been restricted.

Last month, the H5N1 virus was recorded in poultry plants in the Krasnodar region, 1,000 kilometres south of Moscow, but the current outbreak is the first near the capital, home to more than 10 million people.

The Russian find follows recent outbreaks in Britain and Turkey, while Hungary reported the first detected case of the strain in January, the first such outbreak in the European Union since mid-2006.

"Poultry plants in the region have been put under strict control for a year," said Vlasov, adding that the Russian public had nothing to fear.

Russian authorities on Saturday said another farm at Podolsk, 40 kilometres south of the capital, was suspected of being contaminated after 44 dead birds were found, but tests had still to confirm this.

And on Sunday a fourth farm at Taldom, 110 kilometres north of Moscow, was under suspicion of housing a further outbreak, with authorities still conducting tests.