SINGAPORE — Secretary of State Mike Pompeo expressed growing exasperation with North Korea on Friday, accusing its government of refusing to respect a promise to President Trump to stop, or even slow, Pyongyang’s nuclear weapons program.

Speaking to reporters while flying to Singapore — a trip intended in part to press Asian counterparts to maintain sanctions against Pyongyang — Mr. Pompeo noted a vague declaration in June by the North Korean leader, Kim Jong-un, to work toward a full denuclearization of the Korean Peninsula.

The chief American diplomat is deeply skeptical that North Korea will give up its nuclear and ballistic missile weapons programs, according to two of his advisers, who said Mr. Pompeo believes he nonetheless must see through the outreach to Pyongyang that he began.

“Chairman Kim made a commitment to denuclearize,” Mr. Pompeo said, adding, “We can see we have still a ways to go to achieve the ultimate outcome with them.”