It is "more important than anything" to keep up the momentum for talks between the United States and North Korea, South Korean President Moon Jae-in told Chinese President Xi Jinping in Beijing on Monday.

North Korea has set a year-end deadline for the United States to change what it says is a policy of hostility amid a stalemate in efforts to make progress on their pledge to end the North's nuclear program and establish lasting peace.

North Korean leader Kim Jong Un and U.S. President Donald Trump have met three times since June 2018, but there has been no substantive progress in dialog while the North demanded crushing international sanctions be lifted first.