Vice President Mike Pence's doctor Jennifer Peña is resigning, the vice president's office confirmed to CBS News.

The reason for the resignation is unclear. Earlier this week, CBS News and other outlets reported that the Pence's doctor had been critical of Ronny Jackson, Mr. Trump's former pick to run the Department of Veterans Affairs, last fall. Pence's press secretary, Alyssa Farah, said the White House Medical Unit informed Pence's office of the resignation.

"The vice president's office was informed today by the White House Medical Unit of the resignation. Physicians assigned to the vice president report to the White House Medical Unit and thus any resignation would go entirely through the medical unit, not the vice president's office," Farah said.

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As CNN first reported and CBS News confirmed, Peña had expressed concerns about Jackson's behavior over a medical incident involving Karen Pence, the vice president's wife. White House Chief of Staff John Kelly and his deputy Joe Hagin were aware of concerns that Jackson made Pence's doctor feel uncomfortable with his "accusatory" tone, "unprofessionalism," and "intimidating" and "aggressive" behavior stemming from a medical incident in September 2017 involving the second lady, according to memos reviewed by a source familiar.

The vice president's doctor, assigned by the U.S. military to the vice president, wrote the series of memos documenting concerns about Jackson's behavior. The medical situation required Mrs. Pence to be transported from Camp David to Walter Reed hospital.

Jackson had asked for reports on Mrs. Pence's condition from physicians who initially treated her at Camp David. While the vice president's physician wrote this was done "without malicious intent to circumvent their medical knowledge," the doctor also noted Jackson went on to share the information with senior medical providers and briefed members of President Trump's White House staff "without specific consultation from the physician to the vice president."

Jackson withdrew his name from consideration for the VA secretary post last month, after Democrats on the Senate Veterans Affairs Committee released unsubstantiated allegations about Jackson's conduct.

— CBS News' Katiana Krawchenko and Kathryn Watson contributed to this report