Following a rapid rapprochement earlier this year that culminated in a historic summit between Donald Trump and Kim Jong Un, progress has stalled with both sides accusing each other of dragging their feet and acting in bad faith.

Critics say North Korea has made no concrete commitments and is unlikely to surrender its atomic arsenal, while Washington's policy of maintaining pressure through isolation and sanctions has left Pyongyang seething.

"The United States has no intention of easing our unilateral or United Nations sanctions" on Pyongyang, stressed Stephen Biegun, the US Special Representative for North Korea.

"However, within the context of the engagement that we have with the DPRK (North Korea), we are prepared to explore number of other things that could build trust.

"We do have a number of initiatives we'd like to look at as we begin the process of denuclearisation in North Korea."

Biegun's comments come a day after US Secretary of State Mike Pompeo voiced hope that a second Trump-Kim summit can be scheduled for early 2019.

The US envoy declined to detail the initiatives, but he has previously said Washington will be more lenient in enforcing a blanket travel ban in cases where Americans are heading to North Korea for humanitarian assistance.

The Trump administration has generally refused to let US aid groups operate in North Korea, seeking both to maximise pressure on the Kim regime and to ensure the safety of US citizens.

Biegun was in Seoul coordinating policies toward the North with his South Korean counterpart Lee Do-hoon, including on a highly symbolic groundbreaking ceremony due next week for reconnecting and modernising cross-border roads and railways on the peninsula.

Lee said they had agreed that the ceremony should go ahead as scheduled, as Seoul seeks to head off possible controversy over breaching sanctions against Pyongyang.