Washington: The United States believes Russia may be conducting low-level nuclear testing in violation of a moratorium on such tests, the head of the Defence Intelligence Agency said on Wednesday.

Zero-yield nuclear tests don't cause mushroom clouds like the one pictured. Credit:Reuters

"The United States believes that Russia probably is not adhering to its nuclear testing moratorium in a manner consistent with the ‘zero-yield’ standard," Lieutenant General Robert P. Ashley said at an arms control forum at the Hudson Institute.

"Zero-yield" tests don't cause the explosive chain reaction triggered in an atomic bomb nuclear warhead.

Negotiated in the 1990s, the Comprehensive Nuclear Test Ban Treaty (CTBT) enjoys wide global support but must be ratified by eight more nuclear technology states — among them Israel, Iran, Egypt and the United States — to come into force.