President Donald Trump is looking forward to another summit with Kim Jong Un, he said Tuesday, after the North Korean leader warned Pyongyang could change its approach to nuclear talks if Washington persists with sanctions.

"I also look forward to meeting with Chairman Kim who realizes so well that North Korea possesses great economic potential!" Trump said in a brief tweet.

The two leaders made global headlines with an unprecedented summit in Singapore in June, where they signed a vaguely-worded pledge on denuclearization of the Korean peninsula.

But progress has since stalled with the two sides disagreeing over what the declaration means, and the pace of US-North Korean negotiations has slowed, with meetings and visits cancelled at short notice.

The North is demanding relief from the multiple sanctions imposed on it over its banned nuclear weapons and ballistic missile programs, and has condemned US insistence on its nuclear disarmament as "gangster-like."

Speculation of a second Trump-Kim summit has ebbed and flowed, with the US president saying that he hoped it would take place early this year.

But a proposed visit by Kim to Seoul before the end of December did not materialise.

On Monday Kim said he might be "compelled to find a new way for defending the sovereignty of the country and the supreme interests of the state"  if Washington continues with sanctions.

But he said he was willing to meet Trump at any time.