North Korea has accused the US of preparing to invade, citing an upcoming joint military exercise with South Korean forces and saying President Donald Trump promised in 2018 to stop that activity.

"It is crystal clear that it is an actual drill and a rehearsal of war aimed at militarily occupying our Republic by surprise attack and rapid dispatch of large-scale reinforcements," North Korea's foreign ministry said on Tuesday.

After the landmark June 2018 summit between the US and North Korea, the US said it would suspend major military exercises, or "war games," with South Korea, but it continues to engage in smaller exercises.

Trump has complained that major military exercises were too expensive and called on South Korea to foot more of the bill.

North Korean leader Kim Jong Un last year said North Korea would avoid testing weapons, but in May it tested a short-range missile.

North Korea on Tuesday said the joint exercise, planned for August, would test the resolve of its promise to cut back on nuclear and missile testing.

A Pentagon spokesman told CNN that the "Alliance 19-2" exercise would show "commitment to the ROK-US alliance and defense of the Korean peninsula through activities that enhance combined readiness."

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North Korea has accused the US of readying for war by holding exercises with South Korea's military and said the Trump administration is "reneging on its commitments."

"It is crystal clear that it is an actual drill and a rehearsal of war aimed at militarily occupying our Republic by surprise attack and rapid dispatch of large-scale reinforcements," North Korea's foreign ministry said on Tuesday.

The US and South Korea are set to conduct the "Alliance 19-2" exercise from August 5 to 23, the South Korean newspaper Chosun Ilbo reported last week.

A North Korean nuclear plant in June 2008. REUTERS/Kyodo

North Korea said that at the June 2018 summit in Singapore, President Donald Trump promised Kim Jong Un that joint military exercises between the US and South Korea would be suspended.

The US, while avoiding large-scale "war games," still engages in smaller exercises with South Korean troops.

By holding the exercise in August, the US would break its commitment, North Korea said.

"With the U.S. unilaterally reneging on its commitments, we are gradually losing our justifications to follow through on the commitments we made with the U.S. as well," the statement said, alluding to the possibility of restarting nuclear tests.

North Korea last year agreed to take steps toward denuclearization and cease testing of ballistic missiles. But in May, it tested a short-range missile.

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A follow-up statement on the foreign ministry's website on Tuesday said:

"The United States is going to conduct a joint military exercise 'Alliance 19-2' with south Korea in contravention of the commitments made at the highest level at a time when the working-level talks between the DPRK and the U.S. are on the agenda, which has been made possible by the DPRK-U.S. summit meeting in Panmunjom."

Kim meets US President Donald Trump at a summit in Singapore in June 2018. Getty

Lt. Col. Dave Eastburn, a Pentagon spokesman, confirmed to CNN that the exercise would go ahead.

Eastburn said that US and Republic of Korea forces "are preparing to conduct a combined training program this fall" and that it "has been adjusted to maintain readiness and support diplomatic efforts."

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"This routine combined training demonstrates the United States' commitment to the ROK-US alliance and defense of the Korean peninsula through activities that enhance combined readiness," Eastburn said.

South Korean marines take part in a military exercise on South Korea's Baengnyeong Island on September 7, 2017. South Korean Marine Corps/Yonhap via REUTERS

In March, Trump said that major military exercises with South Korea were becoming "very expensive" and that the US was paying for most of them.

"I was telling the generals, I said: Look, you know, exercising is fun and it's nice and they play the war games. And I'm not saying it's not necessary, because at some levels it is, but at other levels it's not," he said.

On Tuesday, Trump said that the upcoming exercise was not an issue and that background talks with North Korea were progressing well.

"We'll see what happens," Trump said. "At some point — I'm in absolutely no hurry — we can probably do something that will be very good for them and for everybody and the world."

Trump and Kim have met three times during Trump's presidency. They gathered in June 2018 for the nuclear summit in Singapore; in February 2019 in Hanoi, Vietnam; and in June at the Demilitarized Zone separating North Korea and South Korea.