Will walk out if meeting with Kim Jong-un doesn't go well: Trump

US President Donald Trump has warned that if his planned talks with North Korean leader Kim Jong-un are "not fruitful" he will "walk out".

Trump said he will be meeting with Kim in the coming weeks to discuss the de-nuclearisation of the Korean Peninsula.

At a joint news conference, Trump and Japanese PM Shinzo Abe yesterday said maximum pressure must be maintained on North Korea over nuclear disarmament.

"If we don't think it's going to be successful.. we won't have it. We won't have it. If I think it's a meeting that is not going to be fruitful, we are not going to go," Trump said.

"If the meeting, when I'm there is not fruitful, I will respectfully leave the meeting and will continue what we are doing or whatever it is that we'll continue, but something will happen," Trump said a day after he told reporters that he is likely to meet Kim in June or before that.

Officials from the two countries are looking at five different venues for the meeting. None of them are in the US.

"Hopefully, that meeting will be a great success and we're looking forward to it," Trump said, adding that it would be tremendous for the world if the meeting went well.

Trump expressed hope that the Korean Peninsula could live together "in safety, prosperity, and peace" following a series of meetings between North Korea and South Korea.

"This is the destiny of the Korean people, who deserve and have gone through so much over the years. We hope it all works it and we'll be trying very hard," he added.

North Korea has been isolated for decades because of its alleged human rights abuses and its pursuit of nuclear weapons, in defiance of international laws and UN sanctions.

It has carried out six nuclear tests, and has missiles that it says could reach the US mainland.

Trump said the release of three American prisoners in North Korea would be among the topics of his discussion with Kim.

Trump yesterday had confirmed that CIA Director Mike Pompeo had made a secret trip to North Korea to meet Kim.

He said Pompeo had forged a "good relationship" with Kim - whom the US president was last year calling "little rocket man" - and that the meeting had gone "very smoothly".

The visit marked the highest-level contact between the US and North Korea since 2000.

Trump pat himself on the back over North Korea and said his administration had achieved what his predecessors could not.

"For many years they have been talking to North Korea and nothing has happened. This should have been taken care of by past administrations when they were not nearly so far along. But we put unbelievably powerful sanctions on, and many other things," said Trump.

The Japanese prime minister backed Trump for his efforts regarding North Korea and demanded complete denuclearisation of North Korea.

"Based on such (past) lessons learned, both the US and Japan, together with the international community will demand for all weapons of mass destruction of ballistic missiles complete verifiable and irreversible dismantlement of weapons of mass destruction and ballistic missiles to North Korea," Abe said.

"By envisioning multiple scenarios, we carefully thought out our policies and directions at a concrete and detailed level. Just because North Korea is responding to dialogue there should be no reward," Abe said.

The Japanese prime minister demanded that maximum pressure be maintained and actual implementation of concrete actions toward de-nuclearisation be demanded from North Korea.

Abe said in his talks with Trump, the two countries have reached agreement regarding the upcoming US-North Korea summit.

"We hope that it will lead to the resolution of weapons of mass destruction, nuclear missile..., he said.