The party meeting was set to continue on Monday, and cover a variety of domestic and external issues, such as how to revive the country’s agriculture and other moribund industries, the news agency reported.

Since assuming power in 2011 after the death of his father, Kim Jong-il, Kim Jong-un has accelerated his country’s nuclear weapons and missile programs. North Korea has conducted four of its six underground nuclear tests since 2011, and it conducted three intercontinental ballistic missile tests in 2017.

But at a Central Committee meeting in April 2018, Mr. Kim declared that with its nuclear force successfully built, North Korea would shift its focus to economic development and halt all nuclear and intercontinental ballistic missile tests.

Two months later, he met Mr. Trump in Singapore for the first summit meeting between the sitting leaders of North Korea and the United States. Afterward, North Korea sounded victorious, and Mr. Kim promised to “work toward complete denuclearization of the Korean Peninsula.” Mr. Trump in turn promised the North security guarantees and “new” relations.

But the mood soon soured as the governments began negotiating the details of what incentives Washington should offer in return for the North’s denuclearization and the timeline for doing so. The North demanded the immediate lifting of United Nations sanctions. Washington, however, insisted that North Korea first dismantle its nuclear program.

A second meeting between Mr. Kim and Mr. Trump, held in Vietnam in February, ended without an agreement, and North Korea later warned that Washington must offer a “new calculation” and create a breakthrough in the stalled negotiations by the end of the year.

Turning up the pressure, the North has resumed weapons tests, launching 27 mostly short-range ballistic missiles and rockets since May and warning of more provocative tests to come. It warned this month that it was entirely up to the Trump administration “what Christmas gift it will select to get,” and conducted two ground tests at its missile engine test site to bolster what it called its “nuclear deterrent.”