US lawmakers are preparing to question President Trump's top intelligence official over a whistleblower complaint that sparked an impeachment inquiry.
Acting national intelligence director Joseph Maguire initially refused to share the complaint with Congress.
It refers to a controversial phone call between Mr Trump and the Ukrainian president, US media report.
In the call, Mr Trump pushes Volodymyr Zelensky to investigate corruption claims involving the son of Joe Biden.
Mr Biden – the leading Democratic presidential hopeful – says a rough transcript of the conversation released on Wednesday shows the president betrayed his oath of office.
Democrats opened an impeachment inquiry against the president on Tuesday, accusing Mr Trump of seeking foreign help in the hope of smearing Mr Biden and of using military aid to Ukraine as a potential bargaining tool.
President Trump has dismissed the impeachment proceedings as a "hoax" and a "witch-hunt".
The whistleblower's formal complaint was still classified on Wednesday, but some US politicians had been allowed to see it, and senior Democrats called for its immediate release.
A House of Representatives vote to impeach the president could trigger a trial in the Senate on whether to remove Mr Trump from office.
Congress's investigation focuses partly on whether Mr Trump abused his presidential powers and sought to help his own re-election by seeking the aid of a foreign government to undermine Mr Biden.
Mr Trump denies putting pressure on Mr Zelensky.
What did Trump say about Biden in the call?
According to notes of the 25 July phone call, President Trump asked his Ukrainian counterpart, Volodymyr Zelensky, to look into corruption claims involving the son of Joe Biden, Mr Trump's possible rival in next year's presidential election. There is no evidence of any wrongdoing by the Bidens.
Mr Trump discusses with newly elected Mr Zelensky the 2016 removal of a prosecutor, Viktor Shokin, according to the notes. He then goes on to discuss Mr Biden's son, Hunter Biden, and the fact that Mr Biden allegedly stopped the prosecution of his son.
On the call, the US president also asks Mr Zelensky to work with US Attorney General William Barr and Mr Trump's personal lawyer, Rudolph Giuliani, to look into the matter, according to the notes.
The Department of Justice said on Wednesday that Mr Trump had not spoken to the attorney general about having Ukraine investigate Mr Biden, and Mr Barr had not communicated with Ukraine.
What has Mr Zelensky said about the call?
The Ukrainian leader has said he thought only Mr Trump's side of their phone call would be published.
"I personally think that sometimes such calls between presidents of independent countries should not be published," he told Ukrainian media in New York, Reuters news agency reports.
Mr Zelensky also said Hunter Biden's case was "one of many" he discusses with foreign leaders.
"For me, this is one of numerous cases that I talk about with the leaders of other states, if they ask me," he is quoted as saying by the Interfax-Ukraine news agency.
"Sometimes, these cases are being investigated or have not been invRead More – Source