US National Security Advisor HR McMaster met with council ambassadors in New York, a few days after President Donald Trump agreed to a summit meeting with North Korean leader Kim Jong Un.

"We are all agreed that we are optimistic about this opportunity," McMaster told reporters after the closed-door meeting at the US mission to the United Nations.

"But we are determined to keep up the campaign of maximum pressure until we see words match with deeds, and real progress toward denuclearization."

Trump agreed last week to a first face-to-face meeting with Kim, which could take place by the end of May, raising hopes for a diplomatic breakthrough after the two leaders spent months hurling insults and threats at each other.

During the meeting with the ambassadors, McMaster pointed to three UN sanctions resolutions adopted by the council as key in the campaign to bring North Korea to the negotiating table, according to a council diplomat.

McMaster said the council had shown "unity and resolve that has us now at the point where we may be able to pursue a diplomatic solution on the complete denuclearization of the Korean peninsula."

The Security Council has imposed tough economic sanctions aimed at choking off revenue to Pyongyang's military programs after Kim's regime carried out a sixth nuclear test and a series of advanced missile launches.

The sanctions resolutions were unanimously adopted following negotiations with China, Pyongyang's ally.

US Ambassador Nikki Haley singled out China for praise, saying Beijing had been "very helpful" in the push for sanctions, and also cited South Korea and Japan.

The sanctions resolutions ban North Korean exports of commodities and severely restricted shipments of oil and fuel to the isolated state.

Dutch Ambassador Karel van Oosterom, who chairs the council's North Korea sanctions committee, told reporters "we have to continue implementing the sanctions as they stand."

A council diplomat said the US appeal to keep up sanctions pressure showed that Washington remained skeptical about prospects for a deal with Pyongyang on scrapping its nuclear program.

McMaster said the Trump administration wanted to move quickly because of concerns that Pyongyang was steadily progressing toward major advancements in its military programs, said the diplomat, who asked not to be named.

The national security adviser also met with UN Secretary-General Antonio Guterres.