Washington (CNN) The White House refused to provide documents to a nonpartisan congressional watchdog investigating President Donald Trump's decision to withhold US security aid to Ukraine, according to documents released by Democratic Sen. Chris Van Hollen of Maryland on Thursday.

Included in the release is a December 20 letter from the White House responding to an inquiry from the Government Accountability Office by citing a previous legal memo from the Office of Management and Budget defending the military aid freeze.

In the letter, Brian Miller, a senior associate counsel to the President, was responding to a request from the GAO seeking "factual information and legal views" about why the Ukraine aid had been held from acting White House chief of staff Mick Mulvaney and White House counsel Pat Cipollone. Miller informed the GAO that Mulvaney and Cipollone would not be participating in the probe.

"The White House does not plan to respond separately to your letters," he wrote.

News of the White House's refusal to participate in the GAO's investigation comes after the watchdog agency issued its decision earlier this month that the Trump administration had broken the law when it withheld the security aid to Ukraine last year, which had been appropriated by Congress.

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