When he met with representatives of political parties in Seoul on Thursday, President Moon Jae-in of South Korea said that negotiations between the United States and North Korea have recently gained “speed,” with Mr. Pompeo planning to visit North Korea again, according to Yun So-ha, an opposition leader, who briefed reporters on the meeting.

On Thursday, Mr. Pompeo said his team was “continuing to make progress” with the North Koreans, and said he hoped that “we can make a big step here before too long.”