United States President Donald Trump solicited interference from Ukraine to influence the 2020 elections, and the White House intervened to "lock down" the transcript of the call, a whistleblower said in a complaint released on Thursday.
"I have received information from multiple US government officials that the president is using the power of his office to solicit interference from a foreign country in the 2020 US election," the whistleblower, an unidentified intelligence community official, wrote in the complaint released by Congress.
The whistleblower said White House officials had expressed alarm about the gravity of Mr Trump's call with his Ukrainian counterpart, and that they told the whistleblower that they had likely "witnessed the president abuse his office for personal gain."
The report was made public shortly before the scheduled start of a House of Representatives Intelligence Committee hearing at which acting Director of National Intelligence, Joseph Maguire, is to testify after refusing for weeks to share the report with Congress.
The report was declassified and released by the committee after weeks of controversy over the matter, which helped lead House Speaker Nancy Pelosi to launch a formal impeachment inquiry into the Republican president.
Mr Trump has denied wrongdoing.
A law required that the report be sent to lawmakers after an inspector general determined that it was urgent and credible.
Shortly before the hearing, the intelligence committee's chairman, Democratic Representative Adam Schiff, announced that it had received the declassified complaint and released it to the public.
"This complaint should never have been withheld from Congress. It exposed serious wrongdoing, and was found both urgent and credible by the Inspector General," Schiff said in a statement.
The whistleblower complaint concerns a July 25 telephone call in which Trump pressed Ukrainian President Volodymyr Zelenskiy to investigate Joe Biden, the 2020 Democratic presidential front-runner, and his son Hunter, who had worked for a company drilling for gas in Ukraine.
"In the days following the phone call, I learned from multiple US officials that senior White House officials had intervened to 'lock down' all the records of the phone call, especially the official word-for-word transcript of the call that was produced as is customary by the White House situation room," the complaint says.
The anonymous whistleblower says that despite his or her not being present for the call, multiple White House officials shared consistent details about it.
The document, with its precise detail and clear narrative, will likely accelerate the impeachment process and put more pressure on Mr Trump to rebut its core contentions and on his fellow Republicans to defend him. The complaint also provides a road map for corroborating witnesses, which will complicate the president's effort to characterize the findings as those of a lone partisan out to undermine him.
Mr Trump immediately tweeted, "The Democrats are trying to destroy the Republican Party and all that it stands for. Stick together, play their game and fight hard Republicans. Our country is at stake." The tweet was in all capital letters.