The US ambassador to the European Union says secretary of state Mike Pompeo was "in the loop" that Donald Trump conditioned a White House meeting and military aid for Ukraine on an investigation being announced into his political opponents.
In potentially devastating testimony that could threaten Mr Trump's presidency, Gordon Sondland said: "Was there a quid pro quo? ... the answer is yes.
Mr Sondland described Mr Trump in May telling him along with energy secretary Rick Perry and then-US special envoy to Ukraine Kurt Volker to work with Mr Giuliani on Ukraine policy at a time when the former New York mayor was working to get the Ukrainians to do the politically motivated investigations.
The inquiry focuses on a 25 July phone call in which Mr Trump asked Ukraine's president Volodymyr Zelenskiy to carry out two investigations.
One involved Joe Biden and his son Hunter, who had worked for Ukrainian energy company Burisma. The other involving a debunked conspiracy theory promoted by some Trump allies that Ukraine, not Russia, interfered in the 2016 US election..
He said he sent an email to Lisa Kenna, an executive assistant at the Department of State, on 11 August, saying that he'd helped to negotiate a statement from Mr Zelensky, and said "the contents will hopefully make the boss happy enough to authorise an invitation (to the White House)".
She replied: "Gordon, I'll pass to S," meaning Mr Pompeo.
Later that month, Mr Sondland discussed with Mr Pompeo the possibility of pushing Mr Zelensky to pledge during a planned meeting with Mr Trump in Warsaw that he would take the steps being sought by Mr Trump.
Mr Pompeo said he approved the plan, it's claimed, but Mr Trump later cancelled his trip to Poland.
The disclosures tie Mr Pompeo closely to the Trump administration’s pressure campaign on Ukraine.
Mr Pompeo was among those who listened in on a call between the two leaders on July 25, when Mr Trump explicitly asked Mr Zelensky for investigations into former vice president Joe Biden.
Mr Sondland said he worked with Mr Trump's personal attorney Rudy Giuliani on Ukraine issues on "the president's orders," detailing Trump's active participation in a controversy that threatens his presidency.