"Donald Trump has denied a report alleging he made a promise to a foreign leader, which sparked a whistleblower's formal complaint," the report said.
Earlier this month, before the whistleblower's complaint came to light, House Democrats launched an investigation into Trump and his lawyer Rudy Giuliani's interactions with Ukraine.
Three Democratic panel heads - Eliot Engel (foreign affairs), Adam Schiff (intelligence) and Elijah Cummings (oversight) - said Trump and Giuliani had attempted "to manipulate the Ukrainian justice system to benefit the president's re-election campaign and target a possible political opponent."
"They allege that Mr Trump and Mr Giuliani tried to pressure the Ukrainian government into investigating Joe and Hunter Biden," the report reads.
The complaint is reported to relate to a July phone call with Zelensky.
Democrats are trying to get the complaint turned over to Congress, with the details still unknown.
However, some reports allege that Trump asked Zelensky to investigate Joe Biden and his son Hunter - who previously served on the board of a Ukrainian gas company - in return for continued U.S. military support.
Joe Biden is currently the frontrunner to be the Democratic candidate competing against Trump in the 2020 presidential election.
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