Kim committed to work toward "complete" denuclearization of the Korean Peninsula in exchange for security guarantees from the US.

"I'm optimistic that we'll come away from that with better understandings, deeper progress, and a plan forward not only for the summit between the two leaders, but for us to continue the efforts to build out a pathway for denuclearization," Pompeo said during a news conference at the State Department.

North Korea's foreign minister said last weekend there was "no way" the regime would disarm first without seeing trust-building measures from the US.

At issue is whether the US will accept North Korea's demand to jointly declare an end to the 1950-53 Korean War, which ended only with an armistice, not a peace treaty.

Pompeo refused to say whether the topic would be on the table Sunday.

He also rejected the notion, posed by a reporter, that he wants to see North Korea's denuclearization by the end of Trump's term in January 2021.

"We want it fast, but we're not going to play the time game," Pompeo said, echoing Trump's remarks from last week. "My comment about 2021 was not mine. I repeated it, but it was a comment that had been made by the leaders who'd had their inter-Korean summit in Pyongyang. They'd talked about 2021 when they were gathered there, and so I was simply reiterating this as a timeline that they were potentially prepared to agree to."

South Korean President Moon Jae-in held a third summit with Kim in mid-September to break the deadlock in negotiations between Washington and Pyongyang. Kim was quoted as telling a South Korean presidential envoy ahead of that meeting that he would like to achieve denuclearization before the end of Trump's term.

Pompeo issued a statement in response to the last inter-Korean summit, saying the US was prepared to "immediately" engage in talks with the North "to transform US-DPRK relations through the process of rapid denuclearization of North Korea, to be completed by January 2021, as committed by Chairman Kim, and to construct a lasting and stable peace regime on the Korean Peninsula."

Trump said a week later that "it doesn't matter" if it takes two years, three years, or five months to denuclearize the regime.

DPRK is short for North Korea's formal name, the Democratic People's Republic of Korea.

"This is a long-term problem. This has been outstanding for decades," Pompeo said. "We've made more progress than has been made in an awfully long time. And importantly, we've done so in a condition which continues to give us the opportunity to achieve the final goal, that is the economic sanctions continue to remain in place, the core proposition; the thing which will give us the capacity to deliver denuclearization isn't changing."

The United Nations Security Council, he said, is united on the need to keep the sanctions in place.

"The Russians and the Chinese had some ideas about how we might begin to think about a time when it would be appropriate to reduce them, but to a country, they were supportive of maintaining the UN Security Council resolutions and the sanctions that underlay them," Pompeo said of last week's Security Council meeting on North Korea.

Pompeo will be making his fourth trip to Pyongyang this year.

He will then travel to Seoul the same day to meet with South Korean President Moon Jae-in and Foreign Minister Kang Kyung-wha. (Yonhap)