A South Korean official in charge of the peace regime issue left for the United States on Wednesday to hold a "working group" meeting.

Rhee Dong-yeol, Director General of the foreign ministry's Korean Peninsula peace regime bureau, plans to meet with Alex Wong, Deputy Assistant Secretary of state for North Korea, in Washington, D.C. on Thursday, South Korean News Agency (Yonhap) reported.

They will be joined by several other officials of the two sides handling North Korea affairs in the first face-to-face working group session since the unsuccessful Hanoi summit between the US and North Korea late last month.

Top agenda items include ways to revitalise the denuclearisation process and Seoul's pursuit of a sanctions waiver for the planned video reunions of separated families living on the other side of the Demilitarised Zone (DMZ). Some equipment needs to be brought into the North for the humanitarian project.

The allies are also expected to touch on Seoul's push for inter-Korean economic cooperation, such as the resumption of the Kaesong Industrial Complex and Mount Kumgang tour programme.

However, they won't likely go into detail about the sensitive issue, with Washington-Pyongyang nuclear talks stalled.

In Hanoi, President Donald Trump rejected North Korean leader Kim Jong-un's offer of dismantling the Yongbyon nuclear facilities in exchange for sanctions relief.

South Korea has stressed that it will seek economic cooperation with North Korea within the framework of the UN-led sanctions on Pyongyang.

In a new report, a panel of UN experts monitoring the implementation of the sanctions said the communist nation has continued illegal activities "enjoying ongoing access" to global financial firms and clandestine ship-to-ship transfers of petroleum products and coal.

The US said it "takes allegations of UN sanctions violations seriously, and all Member States are expected to fully implement UN Security Council resolutions."

The South Korean government hailed the work of the committee.

The report is expected to "be helpful to the effective implementation of sanctions on North Korea," an official at the Ministry of Foreign Affairs said.

Washington's chief envoy for Pyongyang, Stephen Biegun, said his country remains willing to talk with North Korea, but he made clear that it wants a package deal, not an incremental approach favored by Pyongyang.

The Moon Jae-in administration is exploring how to facilitate negotiations between Pyongyang and Washington, while maintaining close coordination with the ally.