PALM BEACH, Florida (BLOOMBERG, AFP, NYTIMES) - President Donald Trump said the US and North Korea have already started direct talks at "extremely high levels" in advance of a planned meeting between the two nations' leaders this summer.

The US has "started talking to North Korea directly," Trump told reporters on Tuesday (April 17) after meeting with Japanese Prime Minister Shinzo Abe at his Mar-a-Lago resort in Florida.

"We have had direct talks at very high levels, extremely high levels with North Korea."

He didn't identify which US officials have been involved.

High-level US officials have spoken to North Korean leader Kim Jong Un directly without involving a third party, a person familiar with the matter said.

The person declined to identify the officials other than as "very senior", but White House Press Secretary Sarah Huckabee Sanders said Trump hasn't spoken directly with the North Korean leader.

Several locations, including Geneva, are being considered as potential summit sites, a US official said. The two countries also are considering venues in Asia and Southeast Asia, said the official, who declined to further identify the sites.

According to CNN, US officials have floated several possible venues over the past month, including: the Mongolian capital Ulaanbaatar; the demilitarized zone between North and South Korea; a neutral European capital like Stockholm or Geneva; a location at sea like Jeju island or a ship; Southeast Asia, including possibly Singapore or Malaysia; the South Korean capital Seoul; or the North Korean capital Pyongyang, a seemingly unlikely choice that no US official has yet ruled out.

Trump also said he's given South Korea his "blessing" to negotiate a peace deal with North Korea.

"People don't realize the Korean War has not ended. It's going on right now. And they are discussing an end to the war," he said.

"Subject to a deal they have my blessing and they do have my blessing to discuss that."

South Korea never formally ended its war with North Korea, though the armed conflict concluded with a cease-fire in 1953.

Setting the stage for a major breakthrough at a series of upcoming summits, Trump said "a great chance to solve a world problem" was within reach on the Korean peninsula.

His comments came just hours after a top South Korean official said North Korea's leader plans to formally announce his willingness to denuclearise his country when he meets South Korea President Moon Jae In next Friday (April 27). The statement is expected to be part of a joint declaration that the two leaders will adopt when they meet on April 27, said Moon's chief of staff, Im Jong Seok.

Negotiators from both Koreas have agreed on a rough framework for the joint declaration, Im said.

Kim told South Korean envoys last month he would be willing to discuss giving up his nuclear weapons if his government no longer felt threatened militarily and its security was guaranteed.

"Although the special envoys have already confirmed a willingness to denuclearise, it will make a difference if the two heads of state will meet and more clearly confirm it and make it a formal statement," Im told reporters on Tuesday.

Trump suggested he was responsible not only for the negotiations on a formal peace treaty ending the war but also the success of this year's winter Olympics in South Korea.

"They've been very generous that without us and without me in particular, I guess, they wouldn't be discussing anything and the Olympics would have been a failure," Trump said.

"As you know North Korea participated in the Olympics and it was really quite an Olympics. It was quite a success. That would not have happened."

Abe praised Trump's leadership, saying his "unwavering conviction as well as his determination" has made talks with North Korea possible.

He said he hoped that Trump would raise the issue of Japanese citizens abducted by North Korea, "a Japanese priority issue," and Trump said he would.

"We will bring up the abductees. We'll bring up many different things," Trump said.

"I know that's been a very big factor for you."

Trump said he will meet with Kim in "early June or before that assuming things go well."

If they don't the summit with the North Korean leader might not happen, he added.

"It's possible things won't go well and we won't have the meetings and we'll just continue to go on this very strong path we have taken," Trump said.

The US, Japan and South Korea have forged an alliance to get Kim to abandon his nuclear weapons programme.

Abe is expected to press Trump during their summit for a sense of what he hopes to accomplish with the meeting, and to underscore what protections Japan is seeking.

"Japan and ourselves are locked and we are very unified on the subject of North Korea," Trump said.