In this Feb. 13, 2019, photo, North Korean Foreign Minister Ri Yong Ho meets his Vietnamese counterpart Pham Binh Minh at the Mansudae Assembly Hall in Pyongyang, North Korea. (AP Photo)

UNITED NATIONS-- North Korean Foreign Minister Ri Yong Ho will not attend the annual gathering of world leaders at the United Nations later this month "due to his schedule," the country's mission to the U.N. told Reuters on Wednesday.

Ri has attended the high-level meeting of the U.N. General Assembly in New York for the past three years. North Korea was initially listed on a tentative speaking schedule - dated July 10 - to again be represented at ministerial level, but a revised agenda issued on Friday downgraded Pyongyang's representation.

North Korea's U.N. Ambassador Kim Song is now expected to address the 193-member world body on Sept. 30, the second last speaker for the week-long gathering.

The United States is trying to kick-start stalled talks with North Korea aimed at dismantling Pyongyang's nuclear and missile programs. The U.N. Security Council has unanimously ratcheted up sanctions on North Korea since 2006 in a bid to choke funding for those programs.

North Korea's U.N. mission appeared to play down the absence of Ri, the country's former chief nuclear negotiator, saying Pyongyang has been represented at various levels in the past.

The U.S. State Department did not immediately respond to a request for comment. North Korean ally and neighbor China has encouraged the talks process and China's top diplomat, State Councillor Wang Yi, visited Pyongyang this week.

U.S. President Donald Trump has met with North Korea leader Kim Jong Un three times, most recently in June when he became the first sitting U.S. president to set foot in North Korea at the Demilitarized Zone (DMZ) between the two Koreas.

They agreed then to reopen working-level negotiations, but that has not happened and since February North Korea has demanded that U.S. Secretary of State Mike Pompeo be replaced with a "more mature" person in the U.S. negotiating team, while lauding the rapport built between Kim and Trump.

Last month Ri called Pompeo the "diehard toxin of the U.S. diplomacy" who employs "hackneyed sanctions rhetoric." Ri and Pompeo met on the sidelines of the U.N. General Assembly last year. They were also both part of a summit between Trump and Kim in Vietnam in February.

North Korea's KCNA news agency on Saturday quoted its vice foreign minister, Choe Son Hui, as saying that a recent remark by Pompeo about "North Korea's rogue behavior" will make talks with the United States more difficult.

The situation has been further complicated by a series of missile launches by North Korea since June, which it says have been in protest against U.S.-South Korea joint military exercises and the adoption of new weapons.

The U.N. Security Council has met twice behind closed-doors at the request of Britain, France and Germany to discuss the launches. The 15-member council demanded in 2006 that Pyongyang suspend its ballistic missile program and stop launches.