Diplomats say the North Koreans have canceled follow-up meetings, demanded more money and failed to maintain basic communications, even as the once-isolated regime’s engagements with China and South Korea flourish.

Meanwhile, a missile-engine testing facility that Trump said would be destroyed remains intact, and U.S. intelligence officials say Pyongyang is working to conceal key aspects of its nuclear program.

The lack of immediate progress, though predicted by many analysts, has frustrated the president, who has fumed at his aides in private even as he publicly hails the success of the negotiations.