Joseph Yun, the U.S. special representative for North Korea, is set to step down, the State Department said on Monday, in a move that comes as Kim Jong Un’s regime says it’s willing to hold talks with Washington.

With no ambassador in place in Seoul, Yun’s departure for “personal reasons” after more than 30 years of service leaves another hole in the American diplomatic service at a critical time. A North Korean official told South Korea this week that the door was open for dialogue, and Washington said it was willing to talk while maintaining its stance of maximum pressure on Pyongyang.

The State Department also does not have a confirmed assistant secretary for East Asian and Pacific Affairs.

Yun, who took up his post in 2016, advocated engagement with North Korea, even when the isolated regime launched sophisticated missiles and conducted underground nuclear tests. During his tenure, he helped to secure the release of Otto Warmbier, an American student detained by the North. He died shortly after returning to the U.S. Doctors said he had suffered a “severe neurological injury” of unknown cause while in North Korean custody.

“We are sorry to see him retire, but our diplomatic efforts regarding North Korea will continue based on our maximum pressure campaign to isolate the DPRK until it agrees to begin credible talks toward a denuclearized Korean peninsula,” State Department spokeswoman Heather Nauert said.

Yun’s resignation raises further questions over the Trump administration’s North Korea policy. Victor Cha, Trump’s original choice to be U.S. ambassador to South Korea, was dropped as a candidate after it was reported that he had privately expressed disagreement with the administration’s North Korea policy.

Cha, a former White House official, warned in an essay last month against hitting the Kim regime with a targeted military strike, ” a bloody nose.” There were reports that a limited strike was under consideration to counter the North’s nuclear threat. But earlier this month, National Security Adviser H.R. McMaster denied that such a strategy existed.

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