Donald Trump released security aid to Ukraine on the proviso Kiev publicly declared it would carry out politically motivated investigations that he sought, a top diplomat has testified he was told.
William Taylor, the most senior US diplomat in Ukraine, gave closed-door testimony to the three Democratic-led House of Representatives committees leading an impeachment inquiry against the president.
The Washington Post posted a copy of Mr Taylor's opening statement online.
In it he described a phone conversation he had with Gordon Sondland, the US envoy to the European Union, who told him that Mr Trump had made the release of the withheld aid contingent on Kiev making public declarations that it would investigate domestic political rival Joe Biden and his son Hunter Biden as well as an issue relating to the 2016 election.
In it he said: "During that phone call, Ambassador Sondland told me that President Trump had told him that he wants President Zelenskiy to state publicly that Ukraine will investigate Burisma and alleged Ukrainian interference in the 2016 election."
The "alleged Ukrainian interference" is a reference to a disproven conspiracy theory that it was Ukraine, and not Russia, that interfered in the 2016 US election and that a Democratic National Committee (DNC) computer server is in Ukraine.
US intelligence agencies and a special counsel investigation concluded that Russia used a campaign of hacking and propaganda to undermine Democratic candidate Hillary Clinton and boost Mr Trump's candidacy in 2016.
The House investigation is focusing on the president's request during a 25 July phone call with Ukrainian President Volodymyr Zelenskiy that he investigate the Bidens.
He made the request - described by Democrats as an improper invitation for foreign interference in an American election - after withholding $391m (£303.5m) in security aid approved by the US Congress to help combat Russia-backed separatists in eastern Ukraine.
Ted Lieu, a Democrat from California, described the testimony as "very devastating to Donald Trump".
Mr Taylor's appearance marked another pivotal development in the political drama unfolding in Washington that threatens Mr Trump's presidency even as he pursues re-election in 2020.
And it comes just a day after the president Trump caused outrage after comparing the impeachment inquiry Democrats have brought against him to "a lynching".
He tweeted: "All Republicans must remember what they are witnessing here - a lynching. But we will WIN!"
Lynchings, which were often hangings, were used mostly by whites against black people. They happened mainly in the southern United States, starting in the late 19th century amid rising racial tensions.
"That is a word that we ought to be very, very careful about using," said the highest-ranking African American politician in Congress, Democratic Representative James Clyburn.
"That is one word no president ought to apply to himself."