SEOUL, South Korea — North Korea abruptly postponed high-level talks with South Korea on Wednesday to protest a joint South Korean-United States Air Force drill, and warned that the historic summit meeting between North Korea’s leader and President Trump next month could be jeopardized.
The news injected sudden tension and uncertainty into what had been months of warming relations on the Korean Peninsula. It came weeks before North Korea’s leader, Kim Jong-un, who has raised the possibility of relinquishing his nuclear weapons, is scheduled to confer with President Trump in what would be the first meeting between leaders of both countries.
Mr. Trump, who threatened North Korea last year with “fire and fury” if Mr. Kim attacked the United States with nuclear weapons, has said he hopes the planned June 12 meeting in Singapore will lead to improved relations with North Korea after decades of hostility.
Senior officials from the two Koreas had been scheduled to meet in the so-called “truce village” of Panmunjom on their border on Wednesday to discuss putting in place an agreement to improve ties and ease military tensions between the countries that their leaders signed in a meeting on April 27.
But the North, appearing to catch South Korea off guard, informed the South early Wednesday that it was unilaterally postponing the talks “indefinitely,” said the South’s Unification Ministry, which helps manage relations between the two Koreas.
The North cited as a reason the annual Max Thunder air force drill that South Korea and the United States started last week, the Unification Ministry said.
The North’s official Korean Central News Agency appeared to go further, warning that the United States should “give serious thought” to how the military drill could affect the plan to hold the summit meeting.
“We will be closely watching the attitude of the United States and South Korean authorities,” the news agency said. It said the Max Thunder drill was a “deliberate military provocation” that had violated the inter-Korean summit agreement reached by Mr. Kim and the South Korean president, Moon Jae-in, in their meeting to work toward easing military tensions.
“The South Korean authorities and the United States launched a large-scale joint air force drill against our Republic even before the ink on the historic inter-Korean declaration has dried,” the news agency said. “There is a limit to our good will.”
The North’s move was surprising partly because Mr. Kim had earlier shown flexibility toward joint military exercises between the South and the United States even though the North had used those drills in the past as a reason to avoid talks with the South.
When Mr. Kim met with South Korean envoys in March, he agreed to meet with President Moon the following month, even though a round of joint South Korean-United States military drills was to start in April.
Mr. Kim was quoted by the South Korean envoys then as saying he understood that those exercises must continue.
Those particular drills are over. The United States and South Korean air forces started the new round of annual drills last Friday.
In Washington, the State Department spokeswoman, Heather Nauert, said the United States had no information about North Korea’s postponement of the meeting with the South.
“Kim Jong-un had said previously that he understands the need and the utility of the United States and the Republic of Korea continuing in its joint exercises,” Ms. Nauert said, using South Korea’s official name. “They are exercises that are legal, they’re planned well, well in advance.”
Ms. Nauert also said the United States had received no notification of any possible change in plans for the summit meeting next month.
“We will continue to go ahead and plan the meeting between President Trump and Kim Jong-un,” she said.
The Pentagon described the Max Thunder exercise as “recurring” and “annual” to maintain military readiness to defend South Korea. “The defensive nature of these combined exercises has been clear for many decades and has not changed,” said Col. Rob Manning, a Defense Department spokesman.
In their March meeting, Mr. Kim told the South Korean envoys that he hoped the United States and South Korea would “readjust” their annual military drills “when the situation stabilizes,” according to the envoys.
Tensions on the divided Korean Peninsula have eased considerably since Mr. Kim began a fast-paced string of diplomatic overtures in recent months, starting with his decision to send North Korean athletes to the Winter Olympics held in the South in February.
Last month, North Korea announced an end to all nuclear and long-range missile tests. Last week, it freed three Americans held in North Korea, sending them home with Mr. Trump’s new secretary of state, Mike Pompeo.
This week, the North invited international journalists to watch its engineers shut down its only-known nuclear test site later this month.
The two Koreas have also started dismantling loudspeakers they have used to blare propaganda broadcasts across the border.
The Trump administration has said its policy of applying “maximum” pressure and sanctions would continue until North Korea takes substantial measures toward denuclearization.
That policy has included increasingly bold joint military exercises with South Korea, including sending multiple aircraft carriers near the Korean Peninsula and flying strategic bombers near the eastern coast of North Korea.
In recent weeks, as they engaged North Korea in dialogue, the United States and South Korea have tried not to advertise their joint drills in order not to provoke the North. But South Korean media have reported that this year’s Max Thunder drill would include eight F-22 Raptor stealth fighter jets and two B-52 Stratofortress bombers.
North Korea has been particularly sensitive about exercises that involve these nuclear-capable aircraft and naval vessels, citing them as a reason for developing its own nuclear deterrent.
North Korea has long demanded that the United States not deploy these weapons around South Korea as one of the conditions for making the Korean Peninsula “nuclear free.” It had been widely expected to push that demand again in any discussions about the terms of denuclearization.
Megan Specia and Rick Gladstone contributed reporting from New York, and Gardiner Harris and Lara Jakes from Washington.