US President Donald Trump has hailed his personal relationship with North Korean leader Kim Jong-un and says there is no reason to resume war games with South Korea.

Key points: White House statement says Mr Trump sees no reason to spend money on war games

White House statement says Mr Trump sees no reason to spend money on war games Mr Trump said it "is not helpful" to dealings when China provides aid to North Korea

Mr Trump said it "is not helpful" to dealings when China provides aid to North Korea South Korea's defence ministry said no decision made about drills later this year

Mr Trump's statement came just days after cancelling a planned visit to North Korea by his top diplomat, and a day after US Defence Secretary Jim Mattis hinted that the military drills, which North Korea denounces as rehearsals for invasion, could resume.

Mr Trump tweeted a White House statement in which he once again questioned China's role in helping to resolve the crisis over North Korea's development of nuclear weapons that threaten the United States.

Donald Trump met Kim Jong-un in June to make an agreement on denuclearisation. ( AP )

The statement said Mr Trump believed North Korea was under "tremendous pressure" from China, but Beijing was also supplying Pyongyang with "considerable aid," including fuel, fertiliser and commodities.

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"This is not helpful!" the statement said.

"Nonetheless, the President believes that his relationship with Kim Jong-un is a very good and warm one, and there is no reason at this time to be spending large amounts of money on joint US-South Korea war games," it added.

The statement added that Mr Trump can restart the games at any time and that "if he does, they will be far bigger than ever before."

The White House Statement also said that the US trade dispute with China and other differences will be resolved and that Mr Trump's relationship with "China's great President Xi Jinping" remains very strong.

Mr Trump caught many American military planners off guard when he announced after an unprecedented summit with Mr Kim on June 12 that the United States was suspending this summer's joint military drills with South Korea, while North Kore would move to denuclearise.

The move was broadly criticised as a premature concession to North Korea, which has resisted US efforts to persuade it to give up its nuclear weapons.

On Tuesday, Mr Mattis noted that the suspension of joint military drills with South Korea as a good-faith gesture to North Korea was not open-ended.

On Wednesday, he reiterated that no decisions had been made about suspending any future exercises and stressed the importance of the US alliance with South Korea.

In 2017, the week-long "Vigilant Ace" exercise involved a total of 230 US and South Korean aircraft including stealth jets, according to the US Indo-Pacific Command website.

Sorry, this video has expired US-South Korea exercises usually involve live-fire drills with tanks, aircraft and warships.

South Korea's defence ministry said that nothing has been decided about whether to hold "Vigilant Ace" this year.

Amid stalling talks with North Korea, South Korean President Moon Jae-in nominated the head of the Joint Chiefs of Staff as the country's new defence minister on Thursday.

Jeong Kyeong-doo, 58, a former fighter pilot, would take over the ministry as the government seeks to reduce tension and build trust with North Korea.

On Friday, Mr Trump called off a trip to North Korea just hours after Secretary of State Mike Pompeo had announced it, and publicly acknowledged for the first time that his efforts to get Pyongyang to denuclearise had stalled.

North Korea has been seeking relief from tough international sanctions and a formal conclusion to the 1950-1953 Korean War, which ended in an armistice rather than a peace treaty.

But Washington says North Korea must give up its nuclear weapons first.

US intelligence and defence officials have repeatedly expressed deep doubts about North Korea's willingness to give up its nuclear weapons and had not expected Mr Pompeo's trip to yield positive results.

Bombs dropped by US and South Korean jets hit a simulated target during a joint exercise. ( AP: South Korea Defence Ministry )

Reuters