WASHINGTON (Reuters) - A top Pentagon official who oversees policy on Ukraine won’t testify on Friday before the congressional committees leading an impeachment inquiry of President Donald Trump but is expected to do so next week, two sources told Reuters on Thursday.

Laura Cooper’s testimony has been sought by lawmakers interested in her knowledge of efforts by Trump to urge Ukraine to investigate former Vice President Joe Biden, a top candidate for the 2020 Democratic presidential nomination, and allegations the president withheld hundreds of millions of dollars in military aid to Ukraine as part of that effort.

She had been slated originally to testify on Friday but now appears to be likely to do so on Oct. 24, the sources said.