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The top White House official responsible for Russia and Europe has been put on indefinite administrative leave amid a security-related investigation, two U.S. officials and a former U.S. official said.

Andrew Peek when he was deputy assistant secretary of state for Iraq and Iran. State Department

The official, Andrew Peek, who took over the Russia portfolio at the National Security Council in November, had been scheduled to join President Donald Trump at the World Economic Forum in Davos, Switzerland, this week before he was abruptly put on leave, one of the officials said. The officials declined to specify the nature of the investigation.

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Peek did not respond to a request for comment Sunday. A spokesman for the National Security Council declined to comment on his status, which was earlier reported by Axios.

"We do not discuss personnel matters," the spokesman said.

Peek's absence, at least temporarily, creates a void in a key position responsible for pushing back on Russian aggression and coordinating U.S. policy toward Moscow. It adds another jolt of uncertainty to an office that has experienced significant turnover during the past year.

Peek, whose background is in Middle East affairs, took over the Russia and Europe portfolio from Tim Morrison, who was a key witness in House hearings on Trump's impeachment. The Russia and Europe role is the same one that was previously occupied by Fiona Hill, another key impeachment witness during last year’s hearings.

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Before starting his post at the White House, Peek had been a deputy assistant secretary of state overseeing Iran and Iraq in the State Department's Bureau of Near Eastern Affairs. Peek, a former Army intelligence officer, also worked on foreign policy in the Senate before joining the administration.