"We do not want to go through (the) traditional process that happened over the years where you get this gradual kind of approach that the North eventually goes back on," the US envoy to the United Nations Conference on Disarmament, Robert Wood, told reporters.

"That is why we are insisting on concrete steps," he said, adding the US needed to see "bold action" from North Korea.

Wood, who repeatedly clashes with Pyongyang's diplomats at the UN's disarmament forum, said Washington was in the process of finalising its strategy for a possible summit between Trump and North Korean leader Kim Jong Un.

He called the prospects of such a meeting "momentous" and something that "many of us never thought would happen."

The odds of the Trump-Kim summit actually taking place were boosted by the shock news that CIA chief Mike Pompeo had gone to Pyongyang to meet Kim for the most significant US-North Korea contact in almost two decades.

Asked whether the US planned to rely on Trump's skills as a dealmaker in negotiating with Kim, Wood said the president's "abilities are going to be very important, but like anything else it takes two to tango."

"The president is a sharp dealmaker. People should not underestimate him," Wood said. "These are high stakes discussions, assuming they take place."

Wood was briefing reporters ahead of a review meeting of the Nuclear Non-proliferation Treaty (NPT), which North Korea pulled out of in 2003.

The US diplomat noted that despite ongoing diplomatic developments, he still planned to use the upcoming NPT review to maintain "maximum pressure" on North Korea.