MOSCOW, June 15 (RIA Novosti) - North Korea has scaled down activity at its nuclear facilities after announcing plans for a new nuclear test, a source in Russia's General Staff said on Monday citing intelligence data.

"Data currently available, including satellite surveillance data, indicate that the intensity of movement in the area of the nuclear facilities has declined in the last few days," the official said. "This means the North Koreans have either completed preparations for another underground test or opted for a pause."

The UN Security Council on Friday toughened previous sanctions against North Korea and imposed new ones following Pyongyang's nuclear test May 25.

The fifteen Council members supported resolution 1874, which expands the arms embargo and allows searches of the nation's ships on high seas, but does not authorize use of force.

North Korea said on Saturday it would respond with war to attempts by the United States and its allies to isolate the country, and that it would start enriching uranium and using plutonium for military purposes.