Another big hurdle: North Korea still has strict quarantine rules in place following last year’s Ebola outbreak in West Africa. All people who have traveled outside the country — including, apparently, Ri, after his return from Singapore — are required to stay at home for 21 days.

The few foreign arrivals have similarly been quarantined in Pyongyang; their only contact with the world outside their apartments is when a state-appointed doctor comes each day to check their temperatures, said foreigners living in the North Korean capital who have been subjected to the rules. This practice is continuing, even as the Ebola crisis subsides.

But the bigger problem is the crevasse between the countries’ starting positions.

“We have made it very clear publicly that we are open to engagement, substantive dialogue with North Korea about the issue of denuclearization,” Sung Kim said after his meetings in Beijing on Friday.