Acting U.S. ambassador to South Korea Kevin Kim has left his post in Seoul less than three months after his appointment, amid questions about Washington’s approach to the alliance and addressing North Korea issues.

The U.S. Embassy in Seoul confirmed to NK News on Wednesday that Deputy Chief of Mission James Heller is serving as Kim’s replacement, while declining to comment on the reason for Kim’s departure.

James Heller joinedthe embassy in July and previously served as acting deputy assistant secretary for Australia, New Zealand and Pacific Islands in the Bureau of East Asian and Pacific Affairs,