SEOUL, South Korea (AP) — The top U.S. envoy for North Korea has expressed confidence about achieving North Korea's nuclear disarmament.

There are worries about the slow pace of nuclear diplomacy since U.S. Secretary of State Mike Pompeo's fourth trip to Pyongyang earlier this month.

Stephen Biegun, the U.S. special representative for North Korea, was in Seoul on Monday to meet with South Korean officials.

Biegun says he's "absolutely confident" that "the final, fully verified denuclearization of North Korea" is "within the reach."

His South Korean counterpart Lee Do-hoon says "denuclearization process is at a critical juncture and we need to meet up as often as possible."

North Korea has taken some measures like dismantling his nuclear testing sites, but the United States wants the North to take more significant steps toward denuclearization.