"This does not affect background radiation. It poses no health threat," said Alexander Frolov, head of the Federal Service for Hydrometeorology and Environmental Monitoring.

The northeastern wind that is now carrying radioactive discharges from Fukushima away from Russian territory will prevail until mid-May, Frolov said.

"The current meteorological situation is very favorable," he said, adding that after that the wind will change to southwestern.

Radioactive substances have already been registered on the Aleutian Islands and they could also reach the Kuril Islands, Frolov said.

However, he stressed, the concentration would be "hundreds of thousands of times less than background radiation."

Officials in Tokyo have warned parents not to give young children tap water due to increased levels of radiation. Radioactive iodine-131 levels have reached 210 becquerels per liter in certain areas of Tokyo, over double the safe level for infants.

Officials say, however, that the water poses no immediate health risk to adults.

Restrictions on food from areas hit by radiation leaks from Fukushima have also been imposed.

Over 9,000 people have been confirmed dead from the massive earthquake and subsequent tsunami that struck eastern Japan earlier this month. But officials say the final death toll is likely to top 20,000.