Senior US, Japanese and South Korean officials with special responsibility for the North Korean nuclear issue held talks Tuesday, at a time of political flux and policy uncertainty in Washington and Seoul.

"We shared the view that it is more important than ever to keep close cooperation among the three countries," South Korea's nuclear envoy Kim Hong-Kyun told reporters after the meeting in Seoul.

The three envoys get together regularly in each other's capitals and one of their main aims is to shape and maintain a consensus on how best to deal with the growing nuclear weapons threat from Pyongyang.

It's a consensus that is looking particularly frail at the moment.

The trio's meeting in Seoul on Tuesday was the first since the eruption of a major political scandal in South Korea that resulted in parliament voting last week to impeach President Park Geun-Hye.

Park took a hard line with North Korea and was a staunch ally of Washington's policy of "strategic patience" -- essentially a refusal to engage in any significant dialogue unless Pyongyang made some tangible commitment to denuclearisation.

Although Park's impeachment still requires approval by the Constitutional Court, most observers are betting on an early election that could result in a more pro-engagement president entering the Blue House.

- Tectonic shifts -

It is also the first trilateral meeting since Donald Trump became US president-elect -- a result that could presage some tectonic shifts in US foreign policy, including how to deal with the security situation on the Korean peninsula.

In a recent interview that drew expressions of deep concern from Beijing, Trump questioned Washington's traditional "one China policy" -- the cornerstone of decades of Sino-American diplomacy.

Adherence to the policy should be linked to other bilateral issues, Trump argued, citing the need for China to do far more to help pressure North Korea into abandoning its nuclear weapons programme.

"There are, to be frank with you, important domestic transitions going on both in Washington and Seoul and I'm sure like everyone else, North Koreans are watching those transitions carefully," the US nuclear envoy Joseph Yun told reporters in Seoul.

Yun spun the hiatus as an "opportunity" for Pyongyang to reconsider its opposition to denuclearisation.

"But so far of course we have not seen any signs that they want to engage," he added.

Specifically addressing the transition in Washington, Yun said it was inevitable that a new administration would take a "fresh look" at outstanding foreign policy issues.

But he stressed that US policy on North Korea had generally enjoyed broad bi-partisan support.

"Nobody, whether they are Republican or Democrat, has ever said anything but the goal of denuclearisation ... so I'm not really worried about that," he said.

High on Tuesday's agenda was implementation of the new sanctions announced earlier this month by the UN Security Council, following North Korea's fifth nuclear test in September.

The measures aimed at blocking Pyongyang's access to hard currency revenues included a cap on North Korea's coal exports -- a key foreign exchange earner.

The United States, Japan and South Korea followed up by announcing their own unilateral sanctions, which Kim said they would try to coordinate in the most effective way possible.