WASHINGTON (BLOOMBERG) - President Donald Trump has agreed to "alter" the 1953 armistice halting the Korean War if North Korea gives up its nuclear weapons, Secretary of State Mike Pompeo said, revealing an apparent promise from Trump's summit with North Korean leader Kim Jong Un that was not announced at the time.

"He has made very clear his commitment to fully denuclearise his country," Pompeo said of the Chairman Kim during a speech at the Detroit Economic Club on Monday (June 18).

"In return for that, the President has committed to making sure that we alter the armistice agreement, provide the security assurances that Chairman Kim needs."

Before the June 12 summit, Trump raised the possibility that a formal peace treaty ending the Korean War of 1950-1953 could be one outcome of his meeting with Chairman Kim of North Korea's State Affairs Commission.

But the joint statement the pair signed made no such promise.

Instead, it said only that the US and North Korea would "join their efforts to build a lasting and stable peace regime on the Korean Peninsula".

Asked about Pompeo's comment on Monday, a National Security Council official, who asked not to be identified speaking about private deliberations, declined to confirm what Pompeo said. The official said only that the two sides had committed to the building of a peace mechanism whose eventual goal would be to replace the armistice.

MILITARY EXERCISES

It was not the first time the administration disclosed a US commitment from the summit that was not cited in the final document.

Hours after meeting Kim in Singapore, Trump told reporters that the US would suspend military exercises with South Korea as long as North Korea continues down the path toward denuclearisation.

Trump was criticised for suspending the exercises without a major concession in return.

A promise to alter the armistice raises questions because it is not something the US could do on its own: Any formal treaty would probably need a sign-off from other nations, including China, and need ratification from the United Nations Security Council.

Trump hinted to reporters after the Singapore summit that the two sides had come to several agreements that were not mentioned in the joint declaration.

"What we signed today was a lot of things included," Trump said. "And then you have things that weren't included that we got after the deal was signed. I've done that before in my life. And we didn't put it in the agreement because we didn't have time."