U.S. negotiators have been unable to get the North Koreans to offer a substantive pledge on denuclearization up front, which has been the chief demand of the Trump administration.

The issue plagued a May 27 meeting in Panmunjom between U.S. and North Korean diplomats, according to a person familiar with the discussions. The talks began with the North Korean side, led by Choe, saying denuclearization should not be on the table for the Singapore summit — a position rejected by the Americans as a nonstarter.

The two sides did not meet for two days, in part because the North Korean delegation did not have the authority to negotiate without additional guidance from Pyongyang, until reconvening briefly May 30 for a session that made little progress in resolving the impasse.