U.S. Secretary of State Mike Pompeo has established a working group inside the State Department on ways to achieve denuclearization of North Korea, but it doesn't include Pyongyang, a U.S. official said Monday.

The remark by department spokeswoman Heather Nauert came two days after she said U.S. and North Korean officials had set up working groups to deal with verification and other details on ridding the North of nuclear weapons during their talks in Pyongyang.

The launch of the U.S. working group suggests that Pyongyang may not have agreed to launch a joint panel with Washington due to a gap between the two sides over measures to advance denuclearization.

Pompeo and Kim Yong Chol, a vice chairman of the Central Committee of the Workers' Party of Korea, held two days of talks through Saturday, the first high-level meeting since a summit between U.S. President Donald Trump and the North's leader Kim Jong Un on June 12 in Singapore.

"Secretary Pompeo has established a post-Singapore summit working group dedicated to directing the State Department's planning, policy, implementation and verification of our efforts to achieve the denuclearization of North Korea consistent with the Singapore summit's joint statement," Nauert told Kyodo News.

In a joint statement issued after the first-ever U.S.-North Korea summit, Kim committed to the "complete" denuclearization of the Korean Peninsula while Trump promised to provide security guarantees to Pyongyang.

Earlier Monday, Japanese Deputy Chief Cabinet Secretary Yasutoshi Nishimura denied the United States and North Korea had launched working groups on denuclearization, as Nauert told reporters Saturday in Pyongyang.

Speaking on a Japanese television program, Nishimura said the United States will establish a working group inside the State Department, not with North Korea.

According to the department, the working group includes Alex Wong, deputy assistant secretary for East Asian and Pacific affairs, Ben Purser, deputy assistant secretary for international security and nonproliferation, and assists Ambassador Sung Kim who leads U.S. diplomacy toward North Korea.

On Saturday, the North's Foreign Ministry accused the Trump administration of pushing a "unilateral and gangster-like demand for denuclearization," hours after Pompeo said his talks with Kim Yong Chol, a close aide to leader Kim, were "productive."