OZERSK, Russia (AP) _ A small amount of radioactive material leaked out of a container at a nuclear plant near this Ural Mountains town, a plant spokesman said Tuesday.

The amount of cesium-137 isotopes that leaked from the Mayak plant exceeded the state-approved monthly discharge level by 5 percent but posed no contamination danger, Alexander Suslov told the Interfax news agency.

Workers were not exposed to radiation during the accident Monday evening, and no contamination of the plant's grounds was reported, he said.

No further details about the accident were released.

Mayak, also known as Chelyabinsk-40, was founded in the late 1940s to produce plutonium for the first Soviet atomic bombs.