An explosion in a smelter on the site of a Russian nuclear power plant severely injured three people, but radiation levels were normal, the state nuclear agency Rosenergoatom said.

The blast occurred at the Leningrad nuclear power plant in the town of Sosnovy Bor, outside the northern city of St. Petersburg and about 600 kilometers (400 miles) northwest of Moscow. Rosenergoatom said that the smelter was located in the grounds of the plant's second unit. The plant has four units in all.

Three people were injured in the blast, the company said. The Emergency Situations Ministry said that two of the injured had burns over 90 percent of their bodies.