The Trump administration’s top diplomat on European affairs will reportedly resign from the State Department next month, thrusting further uncertainty into an already tense relationship between the White House and the European Union.

A. Wess Mitchell, 41, cited personal and professional reasons for leaving his post in a Jan. 4 resignation letter obtained by The Washington Post. His last day as assistant secretary of State for European and Eurasian affairs is Feb. 15.

The State Department confirmed Mitchell's upcoming resignation on Twitter, praising him as an "effective leader" and "good friend" to U.S. allies and partners in Europe. He will be replaced by Principal Deputy Assistant Secretary Elisabeth Millard on an acting basis, Robert Palladino, a deputy spokesperson for the State Department, tweeted.

Assistant Secretary A. Wess Mitchell has been a valued and effective leader in @StateDept and good friend to our allies and partners in #Europe. We thank him for his service and wish him and his family well. — Robert Palladino (@StateDeputySPOX) January 22, 2019

In his letter, Mitchell said he felt that he had "completed what I set out to do" in his role.

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“As the administration completes its second year in office, I feel that I have completed what I set out to do in taking this position,” he wrote, citing his role in developing the State Department’s European strategy and helping Secretary of State Mike Pompeo Michael (Mike) Richard PompeoHouse panel halts contempt proceedings against Pompeo after documents turned over Outgoing ambassador to China slams Beijing over coronavirus: 'Could have been contained in Wuhan' Hillicon Valley: FBI chief says Russia is trying to interfere in election to undermine Biden | Treasury Dept. sanctions Iranian government-backed hackers MORE transition into his post after the firing of Rex Tillerson Rex Wayne TillersonGary Cohn: 'I haven't made up my mind' on vote for president in November Kushner says 'Alice in Wonderland' describes Trump presidency: Woodward book Conspicuous by their absence from the Republican Convention MORE, according to the newspaper.

“As such, I believe that the time has come for me to spend more time with my young family, who have endured many days without me over the past several months,” he continued, according to the Post.

The State Department did not immediately respond to a request for comment from The Hill.

Mitchell sought to tamp down possible speculation that his resignation came in response to President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE's policies and rhetoric toward European countries.

“I’m fully supportive of him, the job he’s doing, the leadership team here,” he told the Post in an interview. “But I feel like I’ve done what I came in to do. My kids have a greater claim to my time right now than the public does.”

Trump rankled European allies by imposing tariffs on imports from European Union countries and calling the NATO "obsolete."

Mitchell echoed Trump's calls for Europe and other allies to share the costs of defense outlays, but told the Post that the U.S. will stay committed to its major allies.

Mitchell became the first assistant secretary of State in the Trump administration confirmed by the Senate in September 2017. He is the latest in a string of recent senior-level departures from the Trump administration.

Former Secretary of State James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE announced his resignation late last month following President Trump’s surprise announcement that the administration would withdraw U.S. troops from Syria.

Another top Mattis ally, Pentagon spokeswoman Dana White, also left after she announced her resignation at the end of December.

The State Department currently has six of 24 positions awaiting Senate confirmation.

Mitchell, who said he does not yet have another job lined up, cautioned that the U.S. and its allies are "underprepared" for an impending "era of big-power competition."

“We’re entering an era of big-power competition,” he told the paper. “The West, U.S. and our allies are underprepared for that transition.”

— Updated 12:30 p.m.