WASHINGTON (REUTERS) - The Trump administration's top nuclear expert involved in talks on ending North Korea's nuclear weapons programs is leaving the White House as part of a regular rotation, three senior administration officials said on Wednesday (June 20).

The expert, Andrea Hall, has already been replaced by Julie Bentz as acting senior director of the Weapons of Mass Destruction directorate at the National Security Council (NSC), another US official said.

Bentz has a doctorate in nuclear engineering, and has served three times previously on the National Security Council dealing with nuclear policy, the official said.

Hall did not immediately respond to a request for comment.

She joined the National Security Council in June 2016 in the administration of former President Barack Obama and had served in several government positions related to weapons of mass destruction and proliferation since 2003. Her previous position was as an adviser in the Office of the Director of National Intelligence.

An NSC spokesman said that while some leadership positions are filled through political appointment, the vast majority of NSC staff come from other agencies and typically serve for a year.

Hall played a key role in the run-up to a summit between US President Donald Trump and North Korean leader Kim Jong Un in Singapore last week.

Trump has hailed the Singapore summit as a success. Skeptics have questioned whether it achieved anything new, given that Pyongyang appeared to make no new concrete commitments.

US Secretary of State Mike Pompeo said he would likely travel back to North Korea "before too terribly long" to try to flesh out commitments made at the summit.

Pompeo, who has travelled twice to North Korea this year and met Kim for a third time at the June 12 Singapore summit, told a business audience in Detroit this week that Kim had made "very clear his commitment to fully denuclearize his country," but there was still a great deal of work to do.