A forest fire has grown in size near the town of Sarov, home to Russia's top nuclear research center, local media reported Friday.

Authorities have previously said all nuclear fuel has been removed from the center.

The fire, which broke out in a wildlife reserve in Mordovia region, had spread to neighboring Sarov in Nizhny Novgorod region, Itar-Tass news agency reported, citing Mordovia's emergency services chief.

"Fire broke out in an eastern sector of the wildlife reserve two days ago after a lightning stroke. Now it has expanded to pose a certain hazard," Major General Vyacheslav Kormilitsyn said.

Efforts were being taken to contain the fire, said Kormilitsyn, adding that chief of the Volga region emergencies center Igor Panshin had ordered all forces involved in fire fighting operations to work round the clock.

More than 2,600 people and about 200 pieces of machinery are currently involved in fighting the fire at Sarov, a small town 300 km east of Moscow. The town hosts the Russian Nuclear Research Center, which includes an atomic reactor.

Sergei Kirienko, head of Russia's Atomic Agency Rosatom, assured the National Security Council last week there was no danger of radiation contamination because all nuclear fuel had been removed from the Sarov research center.