A senior Adviser to the U.S. Secretary of State Mike Pompeo has stepped down from his duties, according to reports from CNN.

Michael McKinley, a diplomat of over three decades and ambassador to Peru, Colombia, Afghanistan and recently, Brazil, was appointed as an adviser in May 2018.

His resignation comes as Pompeo faces increasing pressure from House investigators over his recently revealed presence on a phone call in which President Donald Trump pressured Ukranian President Volodymyr Zelensky to investigate former Vice President Joe Biden — Trump’s potential Democratic rival — and Biden’s son Hunter. There is no evidence of wrongdoing in Ukraine by Joe or Hunter Biden.

The Washington Post first reported McKinley’s resignation, adding that it came in the midst of growing discontent at the State Department in response to Pompeo’s perceived lack of support for department officials caught up in investigations linked to Ukraine.

Pompeo, who recruited McKinley as an adviser and liaison to the career service, is expected to address McKinley’s departure on Friday, according to the Post.

McKinley has declined to comment.

A person familiar with the situation told the Post that McKinley saw Pompeo as benefiting the department — compared to previous Secretary of State Rex Tillerson — for fostering differing viewpoints and halting Tillerson’s freeze on promotions and limits on department employees’ spouses working abroad.

The Post also reported that while McKinley was not working directly on Ukraine policy, he disapproved of what he saw as Pompeo’s insufficient public support for department officials implicated in Trump’s dealings with Ukraine and subsequently called to testify in House Democrats’ investigation.

McKinley was involved in several policy spheres, holding key roles in foreign policy efforts in Venezuela, Mexico and Afghanistan, the Post reported — the last a key international focus after Trump revealed last month that Taliban leaders had been slated to travel to the US for secret peace talks but that the meeting was canceled as he called off peace talks with the militant group entirely.