The White House has released details of a phone call between President Trump and his Ukrainian counterpart that has triggered a US impeachment inquiry.
It shows Trump asked Volodymyr Zelensky on 25 July to investigate Democratic candidate Joe Biden, whose son worked for a Ukrainian gas firm.
Trump denies withholding US military aid to Ukraine as leverage in a bid to smear his political rival, Mr Biden.
The Trump-Ukraine phone call is part of a whistleblower’s complaint.
Reacting to the controversy on Wednesday morning at the United Nations General Assembly in New York City, Trump said it was the “single greatest witch hunt in American history”.
The Democratic leader of the House of Representatives, Speaker Nancy Pelosi, on Tuesday threw her weight behind an official impeachment inquiry into the president’s actions.
A House vote to impeach the president for “high crimes and misdemeanours” under the US constitution could trigger a trial in the Senate on whether to remove Trump from office.