Russia has deployed extra troops to guard dozens of nuclear facilities across the country in response to recent militant activity including the taking of hostages at a a school in the south of the country.
Russia, the world's second largest atomic power after the United States, has come under international pressure to do more to protect its Soviet-era nuclear facilities against attack.
"After the latest terrorist attacks security services decided to send more interior ministry troops to all nuclear sites across the country," a Russian Atomic Energy Agency spokesman said.
He would not say how many additional troops were sent.
He said the government extended the order right after militants seized a school near rebel Chechnya, taking up to 150 people hostage, and a suicide bomb attack in central Moscow which killed at least nine people.
Russia runs dozens of atomic reactors, uranium enrichment facilities and nuclear research reactors - some in the far-flung corners of Siberia and which are poorly guarded.