Less activity at N.Korea nuclear sites: Russian agency

North Korean soldiers guard the bank of the Yalu River near the Chongsong County of North Korea, opposite the Chinese border town of Hekou June 15, 2009.

MOSCOW (Reuters) - Russian reconnaissance has registered a fall in activity around North Korea nuclear sites in recent days, state-run Russian news agency RIA Novosti reported on Monday, citing a senior military source.

The fall in activity could either signify preparations for a new nuclear test or that North Korea's nuclear forces have taken a break after testing a bomb last month, the source said.

The United Nations Security Council on Friday tightened sanctions against North Korea in response to its May 25 nuclear test, which put it closer to having a working nuclear bomb.

In response, North Korea said it would start a uranium enrichment program and weaponize all its plutonium. Pyongyang also threatened military action if Washington and its allies tried to isolate it.

"Information we have received, some from our space reconnaissance, indicates that the intensity of movement around the nuclear objects has fallen in recent days," RIA Novosti quoted the official in Russia's military command as saying.

"This could be evidence that the North Koreans are preparing to hold their next nuclear test or that they have taken a break," the official said.

(Writing by Conor Humphries; Editing by Peter Millership)