Russia may be violating a ban on the testing of low-yield nuclear weapons capabilities at a site in the Arctic, a top US intelligence official said.

Lt Gen Robert Ashley, the director of the US Defense Intelligence Agency, said Moscow was « probably not adhering to » the rules of a recognised treaty.

He was referring to the Comprehensive Test Ban Treaty (CTBT), a multilateral agreement prohibiting nuclear testing.

Russia, which ratified the treaty in 2008, says it complies with the CTBT.

The US has signed but has not yet ratified the treaty.

« Our understanding of nuclear weapon development leads us to believe that Russia’s testing activities would help it improve its nuclear weapons capabilities, » Lt Gen Ashley said on Wednesday.

He added that the US expected Russia, which he said was likely testing weapons in the Novaya Zemlya islands, to increase its nuclear arsenal « significantly » over the next decade.

But analysts received the statement with scepticism. The Comprehensive Nuclear Test Ban Treaty Organization (CTBTO) said in a statement that it had not detected any unusual activity.

« The CTBTO has full confidence in the ability of the IMS [its monitoring system] to detect nuclear test explosions, », the organisation said in a statement.

The CTBT, which bans nuclear weapons testing anywhere in the world, was adopted by the UN General Assembly in 1996. It sets out nuclear disarmament as a principle but diplomatically avoids the politics of the issue.