The first-ever meeting between a North Korean leader and a sitting US president took place on June 12 last year in Singapore, where Kim Jong Un and Trump signed a vaguely-worded deal to achieve "complete denuclearisation".

But a second meeting in Vietnam in February ended abruptly as the two failed to agree on what the North would be willing to give up in exchange for sanctions relief.

The joint statement from the Singapore meeting "of great historic significance is now on the verge of turning into a dead document as the U.S. shuns its implementation", said the North's official Korean Central News Agency (KCNA).

It added the "arrogant and unilateral policy" of the US would never work with North Korea.

"There is a limit to the DPRK's patience," it said, using the acronym for the North's official name, adding: "Now is the time for the US to roll back its hostile policy."

At the Hanoi meeting, Washington sought a more immediate comprehensive denuclearisation deal while Pyongyang wanted a step-by-step process, and demanded the lifting of key economic sanctions in return for shutting down its Yongbyon nuclear complex, which the US refused.

Since Hanoi, Pyongyang has accused Washington of acting in "bad faith" and given it until the end of the year to change its approach.

Last month the North raised tensions in the region by firing short-range missiles for the first time since November 2017.

South Korean President Moon Jae-in, who was instrumental in brokering the Singapore summit a year ago, said on Monday talks were underway for a third North-US meeting, according to South Korea's Yonhap news agency.

Moon added Pyongyang had refrained from nuclear and long-range missile tests for more than one-and-a-half years.

Trump and Kim continued to express "trust in each other" and "desire for dialogue", he said.