The Trump administration broke the law in holding up more than $200 million in security assistance to Ukraine, a top government watchdog concluded on Thursday, offering new, damning information on President Donald Trump's controversial – and still unexplained – decision that prompted his impeachment late last year.

"The Office of Management and Budget violated the law when it withheld approximately $214 million appropriated to DOD for security assistance to Ukraine," the Government Accountability Office said Thursday in a statement . "The president has narrow, limited authority to withhold appropriations under the Impoundment Control Act of 1974. OMB told GAO that it withheld the funds to ensure that they were not spent 'in a manner that could conflict with the president's foreign policy.' The law does not permit OMB to withhold funds for policy reasons."

News that Trump withheld annual, congressionally approved military assistance funding to the former Soviet country amid its ongoing war with Russia sparked widespread outrage last summer, and confused many top officials overseeing Ukraine policy at the time who did not receive an explanation for the holdup. Trump ultimately released the aid shortly before the Sept. 30 deadline by which it must have been spent.

The question of whether the president used the money as a quid pro quo to get the Ukrainian government to investigate his political rivals – namely Democratic presidential frontrunner Joe Biden along with his son, Hunter Biden – became a central component of a series of investigations conducted by the House of Representatives last fall, ultimately concluding with a vote of impeachment along party lines.

Members of the House appointed by Speaker Nancy Pelosi delivered those articles of impeachment to the Senate on Wednesday.

Congress has approved various forms of military assistance to Ukraine since Russia annexed the Crimean Peninsula and backed separatist forces in the country's eastern reaches in 2014, sparking a war that continues as a simmering conflict with both sides still taking casualties. The American support includes almost $400 million in various forms of financial support each year along with training from U.S. troops operating at facilities in the country's west .

Pentagon spokesman Jonathan Hoffman declined Thursday shortly after the news broke to comment on the specifics of the GAO announcement, citing "a highly politicized situation right now."

In response to a question about the political fallout, Hoffman referenced that the aid was ultimately spent, and that it aligned with the Pentagon's goals of ensuring Ukraine pursues anti-corruption efforts, that allies spend more in assisting Ukraine and that the result benefits the U.S. militarily. He added, "We were able to get the aid out the door as we intended to, so I wouldn't characterize it as a mess."

Rep. Adam Schiff, chairman of the House Intelligence Committee which oversaw one of the impeachment investigations, said in a statement Thursday that the GAO finding should prompt the OMB to cooperate with the Senate impeachment trial having refused to cooperate with his committee's requests for information and testimony.

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"The President was willing to violate the law in withholding security assistance from an ally at war with Russia, a gross abuse of the powers of his office, acts for which he was impeached," the California Democrat said. "President Trump's conduct is all the more egregious because he was not withholding the funds for a policy reason at all, but for the corrupt purpose of seeking foreign help in his reelection campaign."

Top officials tasked with Ukraine policy first found out about the holdup in aid during a routine teleconference a week before a July 25 phone call between Trump and newly elected Ukrainian President Volodymyr Zelenskiy. A representative from the OMB told the officials about the holdup and that it was the president's decision, but did not have any details at the time on the rationale behind the decision.

Memos released as part of the impeachment proceedings indicated there was immediate concern, including within the White House's National Security Council, that the president chose to withhold the money as a way to pressure Zelenskiy during their call to launch an investigation into whether Hunter Biden acted inappropriately during his time on the board of Burisma, a Ukrainian gas company.

Transcripts the White House released of the call show Trump asked Zelenskiy to open the investigations, prompting the newly elected leader to do him "a favor" after first referencing the substantial support the U.S. provides Ukraine.