US academics and former senior officials have met with North Korea's chief nuclear negotiator in Singapore.

The meeting was set to get a feel for each other's positions amid a years-long standoff over the North's nuclear weapons buildup.

Leon Sigal, director of the Northeast Asia Cooperative Security Project at the Social Science Research Council, a US-based nonprofit, told reporters that the meeting will cover the North's nuclear missile programs.

He said "it's two ways of taking each other's temperature."

The US and North Korea have no formal diplomatic ties, but former US officials occasionally meet the North's diplomats in a bid to settle the impasse over Pyongyang's pursuit of a long-range nuclear-armed missile that could hit the US mainland.

North Korea's team was led by Ri Yong Ho, the chief negotiator for six-party denuclearisation talks.

North Korea has indicated willingness to rejoin the long-stalled talks, but has baulked at US demands it first take concrete steps to show it remains committed to the denuclearisation goal.

Earlier this month, North Korea told the United States that it is willing to impose a temporary moratorium on its nuclear tests if Washington scraps planned military drills with South Korea this year.

Washington called the linking of the military drills with a possible nuclear test "an implicit threat," but said it was open to dialogue with North Korea.

Pyongyang is thought to have a handful of crude nuclear bombs and has conducted three nuclear tests since 2006.

But experts are divided on how far the opaque government has come in the technology needed to miniaturise a warhead.