US President Donald Trump asked Ukrainian President Volodymyr Zelenskiy to look into the conduct of former vice president Joe Biden, a memo of a call released by the White House on Wednesday showed.
Democrats have launched a formal impeachment inquiry against Mr Trump, accusing him of trying to pressure Mr Zelenskiy into opening a corruption probe into Mr Biden, the leading Democrat presidential contender.
The US president has admitted withholding millions of dollars in defence aid from Ukraine, but said it was to force Eastern European countries to contribute their share.
The investigation, a first step in a possible impeachment process, was to focus accusations that Mr Biden, as vice president, tried to stop the closure of a Ukrainian company for which his son Hunter worked.
Mr Trump asked Mr Zelenskiy to work with his personal lawyer, Rudy Giuliani, and US Attorney General William Barr.
"I heard you had a prosecutor who was very good and he was shut down and that's really unfair," he told the Ukrainian president in the July 25 call. "A lot of people are talking about that.
"There's a lot of talk about Biden's son, that Biden stopped the prosecution and a lot of people want to find out about that."
As vice president, Mr Biden and other western leaders pressured Ukraine to get rid of the country's top prosecutor, Viktor Shokin, because he was seen as too soft on corruption.
"Biden stopped the prosecution and a lot of people want to find out about that, so whatever you can do with the attorney general would be great," Mr Trump said.
"Biden went around bragging that he stopped the prosecution, so if you can look into it ... it sounds horrible to me."
Mr Trump also asked Mr Zelenskiy to investigate whether his country could find a hacked Democratic National Committee computer server that became an issue in his 2016 campaign against Hillary Clinton.
Mr Trump promised that a "complete, fully declassified and unredacted transcript" of the call would be released.
But what was disclosed on Wednesday morning were notes of the conversation taken by US officials who listened to it.
The five-page memorandum notes that it is “not a verbatim transcript” of the discussion, a disclaimer in its footnote states.
The July call occurred days after Mr Trump directed the US government to withhold about US$391 million in military aid to Ukraine.
Democratic presidential candidate Elizabeth Warren said the transcript was a "smoking gun", especially if it represented the parts of the call that the administration considered acceptable.
In New York, Mr Trump said that the memorandum reflected well on him. He insisted it proved his conversation with the Ukrainian president was a "nothing call".
“The way you had that built up, that call, it was going to be the call from hell,” Mr Trump said. “It turned out to be a nothing call, other than a lot of people said, 'I never knew you could so nice'.
"Part of the problem you have is you have the fake news, you have a lot of corrupt reporting."
Mr Trump also called the impeachment inquiry "a disgraceful thing" and denied pressuring Mr Zelenskiy.
"It's the single greatest witch hunt in American history," he said. "It's a disgraceful thing."
Former presidential candidate Hillary Clinton tweeted that Mr Trump was a "clear and present danger" and urged impeachment.
Republican senator Mitt Romney, who earlier voiced concern about Ukraine allegations, said he found the transcript disturbing.
“My reaction was the same as I had a few days ago, which is this remains deeply troubling and we’ll see where it leads," Mr Romney said. "But my first reaction is it’s troubling."
The administration is also preparing for the possible release of a redacted version of the whistle-blower complaint by an intelligence official, which started the uproar over the phone call, The New York Times reported.
Mr Zelenskiy and Mr Trump were due to meet for the first time on Wednesday on the sidelines of the UN General Assembly.
"Nobody can pressure me because I am the president of an independent country," Mr Zelenskiy told the Russian news channel Rossiya 24.
"The only person who can put pressure on me is my son, who is six years old."