A federal watchdog concluded that President Trump broke the law when he froze assistance funds for Ukraine last year, according to a report unveiled on Thursday.

The White House has said that it believed Trump was acting within his legal authority.

Trump's decision to freeze military aid appropriated by Congress is at the heart of impeachment proceedings against the president that are shifting venues this week from the Democrat-controlled House to the majority-Republican Senate.

The U.S. government’s congressional watchdog determined that the Trump administration violated the law when it withheld hundreds of millions of dollars in security aid to Ukraine in the summer of 2019.

The Government Accountability Office released a nine-page report Thursday concluding the Office of Management and Budget violated the Impoundment Control Act when it held up $214 million appropriated by Congress to the Department of Defense to help Ukraine as it deals with a Russian incursion in the eastern part of its country.

The Trump administration violated the law by withholding military aid to Ukraine, the U.S. Government Accountability Office said in a decision released Thursday.

"In the summer of 2019, the Office of Management and Budget (OMB) withheld from obligation funds appropriated to the Department of Defense (DOD) for security assistance to Ukraine," the non-partisan government watchdog's ruling said.