US President Donald Trump has dismissed a report alleging he made a promise to a foreign leader, something that triggered a formal complaint from an intelligence official.
A report by the Washington Post said the whistleblower found the President’s remark “so troubling” they went to the department’s inspector general.
In a tweet on Thursday, Mr. Trump rejected the allegations as “fake news”.
He said he knew all his phone calls to foreign leaders were listened to by US agencies.
“Knowing all of this, is anybody dumb enough to believe that I would say something inappropriate with a foreign leader,” he asked.
Opposition Democrats are trying to get the complaint handed over to Congress, with the details still unknown.
According to a letter addressed to the House, the complaint consists of a “serious or flagrant problem, abuse or violation of the law” that involves classified information.
It is not yet known who made the complaint, which foreign leader Mr. Trump was speaking to, what promise – if any – was made and whether the President took any action as a result.
But citing officials with knowledge of the matter, the Washington Post and the New York Times both said at least part of the complaint related to Ukraine.
The complaint was filed on August 12, and President Trump had spoken by phone with his Ukrainian counterpart Volodymyr Zelenskyy two and a half weeks prior to that.
House Democrats have been investigating whether Mr Trump and his lawyer Rudy Giuliani tried to pressure the Ukrainian government to investigate former
Vice-President Joe Biden, and his son Hunter Biden, who previously served on the board of a Ukrainian gas company.
Joe Biden is currently seeking the Democratic presidential nomination.