Seoul — North Korea on Tuesday cast doubt on next month’s summit between leader Kim Jong Un and President Donald Trump over joint air force drills taking place in South Korea, which it says are ruining the diplomatic mood.

The sudden announcement by the communist government — issued in the middle of the night in North Korea — said the military exercises were a “provocation” that could affect the fate of the unprecedented summit.

North Korea always reacts angrily to the joint U.S.-South Korea military exercises, considering them a rehearsal for an invasion. But this year, with the sudden burst of diplomacy, had appeared to be different.

The South Korean and U.S. militaries had scaled back and played down the exercises, declining the media the usual access to the drills. North Korea said barely a word about the drills during the computer simulation exercises that took place through April.

But the two-week-long Max Thunder drills between the two countries’ air forces, an annual event that began on Friday, have clearly struck a nerve.

North Korea suggested that the drills were putting the proposed summit between Trump and Kim, scheduled for June 12, in jeopardy.

“The United States will also have to undertake careful deliberations about the fate of the planned North Korea-U.S. summit in light of this provocative military ruckus jointly conducted with the South Korean authorities,” said KCNA, the North’s Korean Central News Agency.

Trump and Kim are due to meet in Singapore, which would be the first time a North Korean leader had met with a sitting U.S. president.

“The United States will look at what North Korea has said independently and continue to coordinate closely with our allies,” said White House press secretary Sarah Huckabee Sanders.

State Department spokeswoman Heather Nauert said the United States had not received notice of any change or cancellation. She said the government is continuing to plan for the summit and is confident that Kim understands the need for the exercises.

A Pentagon spokesman, Army Col. Robert Manning III, said Tuesday that the exercises are part of the U.S.-South Korean alliance’s “routine, annual training program to maintain a foundation of military readiness.”

Manning said the purpose of the exercises is to enhance the alliance’s ability to defend South Korea.

“While we will not discuss specifics, the defensive nature of these combined exercises has been clear for many decades and has not changed,” he said.

North Korea, as it has in the past, disagreed. “This exercise targeting us, which is being carried out across South Korea, is a flagrant challenge to the Panmunjom Declaration and an intentional military provocation running counter to the positive political development on the Korean Peninsula,” KCNA said.

The Max Thunder exercise involves about 100 warplanes, including eight F-22 radar-evading fighters and an unspecified number of B-52 bombers and F-15K jets, according to the South’s main Yonhap News Agency. During last year’s Max Thunder exercises, U.S. and South Korean fighter jets flew an average 60 sorties a day to showcase their firepower.

By mentioning the Panmunjom Declaration, North Korea was referring to the agreement signed last month by Kim and South Korean President Moon Jae-in following their historic summit.

They agreed to work to turn the armistice agreement that ended the Korean War in 1953 into a peace treaty that would officially bring the war to a close, and also to pursue the “complete denuclearization” of the Korean Peninsula.

Trump and his top aides, including Secretary of State Mike Pompeo and national security adviser John Bolton, both previously known for their hard-line views on North Korea, have expressed optimism that a denuclearization agreement can be worked out.

In surprising detail, Pompeo — who says Kim watches foreign news reports — has laid out the economic and development aid that would flow to the North Korean regime if it permanently and verifiably gives up its nuclear weapons program.

But North Korea, despite being run by one totalitarian family for the past seven decades, is not entirely monolithic. It does have its hawks and doves, and analysts speculated that hard-liners in the military, concerned about the sudden talk of denuclearization, might be trying to interfere with the current diplomatic efforts.

At the same time as threatening to scupper the summit with Trump, North Korea canceled talks with South Korean officials that had been scheduled for today, less than 24 hours after agreeing to them.

North Korea had said it would send five senior officials to the border village of Panmunjom for meetings with South Korean officials, the first such talks since the April 27 inter-Korean summit.

They were due to discuss some of the infrastructure aid that South Korea would provide to North Korea as part of their broader detente. The North was going to send Ri Son Kwon, who leads the North Korean agency in charge of inter-Korean exchanges and was present at the summit, while the South was going to send senior officials from the Transport Ministry and forest service.

“Through the inter-Korean high-level talks, [we] will push to lay the groundwork for sustainable development and lasting peace by having in-depth discussions and faithfully implementing the Panmunjom Declaration,” the South’s Unification Ministry said in a statement on Tuesday.

Max Thunder has been held annually in the spring for about 10 years. It features the United States and South Korea flying strike aircraft together from air bases in South Korea and Japan to practice air-to-air combat.