Washington (CNN) The Pentagon's top policy official who warned against withholding military aid to Ukraine last year resigned on Wednesday at the request of President Donald Trump, according to a copy of his resignation letter obtained by CNN.

John Rood, Under Secretary of Defense for Policy at the Pentagon, is the latest senior national security official involved in the Ukraine controversy to be forced out following Trump's acquittal in the Senate impeachment trial, but sources told CNN that he broke with the administration on several issues, in addition to the handling of aid to Ukraine, leading to a loss of support from leadership.

"It is my understanding from Secretary Esper that you requested my resignation from serving as Under Secretary of Defense for Policy. Senior administration officials appointed by the President serve at the pleasure of the President, and therefore, as you have requested, I am providing my resignation effective February 28, 2020," Rood wrote in his letter to President Donald Trump, dated Wednesday.

CNN was first to report Rood's impending departure which was confirmed by Trump in a tweet Wednesday.

"I would like to thank John Rood for his service to our Country, and wish him well in his future endeavors!" Trump wrote, also sharing a story from Bloomberg News which indicated that Rood "faced pressure to resign from some who lost confidence in his ability to carry out Trump agenda."

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