President Donald Trump directly asked about a Ukrainian investigation into his Democratic rival Joe Biden, a top US diplomat has unveiled.
Bill Taylor, the acting ambassador to Ukraine, told an impeachment inquiry that a member of his staff was told Mr Trump was keen to push for the probe.
Mr Trump says he does not recall making the remark. He denies any wrongdoing.
Mr Biden hopes to run against Mr Trump next year. It is illegal to ask foreign entities for help to win an election.
He is accused of withholding US military aid to Ukraine in order to pressure the country’s new president to publicly announce a corruption inquiry into Mr Biden.
Mr Trump has called the inquiry a “witch-hunt”.