• Sanctions remain in full force until US sees positive results: Trump

• Pyongyang may change its approach to talks if sanctions persist: Kim

US President Donald Trump said Sunday negotiations are underway on the location of his next summit with North Korean leader Kim Jong Un, while remaining evasive on its timing.

Trump, who held a historic summit with Kim in Singapore in June, said earlier in the week he had received a "great letter" from the North Korean leader but declined to reveal its contents.

"We are negotiating a location," he told reporters before boarding a helicopter for the presidential retreat at Camp David, Maryland, where he said he would be discussing a trade deal with China.

"It will be announced probably in the not too distant future," he said of a summit with Kim. "They do want to meet and we want to meet and we'll see what happens."

File photo.

"With North Korea, we have a very good dialogue," Trump added, saying he had "indirectly spoken" with Kim.

The latest letter from Kim came after the North Korean leader warned in a New Year's speech that Pyongyang may change its approach to nuclear talks if Washington persists with sanctions.

Trump said Sunday the sanctions remain "in full force and effect" and would do so until the United States saw "very positive" results.

At the first summit between the longtime adversaries in June, Trump and Kim agreed to work toward the Korean peninsula's denuclearization but with little apparent agreement on what that means.

The United States has been pressing for North Korea to get rid of its nuclear weapons before any easing of economic pressure.

Kim, whose family has ruled North Korea with an iron fist for 70 years, wants immediate economic benefits and a formal end to the 1950-53 Korean War.

Trump has cast his first summit with Kim as a major diplomatic victory, and on Sunday repeated his claim that there would be war in Asia had they not sat down to talk.

"Anyone else but me, you would have been at war right now ... You right now would have been at a nice big fat war in Asia with North Korea if I hadn't been elected president."

But progress has stalled since the Singapore summit with the two sides disagreeing over the meaning of their vaguely-worded declaration, and the pace of US-North Korean negotiations has slowed, with meetings and visits cancelled at short notice.