The complaint from an anonymous whistleblower who sparked an impeachment inquiry into U.S. President Donald Trump has been declassified and is expected to be released for public consumption, according to U.S. media reports. 

The reports were supported by a tweet from Republican Representative Chris Stewart. CNN also reported that a deal had also been reached, pending clearances, for the whistleblower to appear before Congress. 

The whistleblower, thought to be an intelligence officer, will speak to lawmakers on condition that Joseph Maguire, the acting director of the national intelligence, approves appropriate security clearances. 

Maguire is scheduled to appear before the House intelligence panel hearing on Thursday.

Read more:

U.S. releases memo of Trump's call

Pelosi announces Trump impeachment inquiry

Behind the Story: Trump, Biden, Ukraine and Giuliani

A transcript of a July 25 call between Trump and Ukrainian President Volodymyr Zelenskiy released on Wednesday revealed the U.S. leader pressed Ukraine's president to probe Joe Biden, a leading challenger for the Democratic presidential nomination in 2020.

The call occurred after Trump had ordered a freeze of nearly 400 million U.S. dollars in American aid to Ukraine, which the administration only later released.

Trump insists there was no quid pro quo, but opponents argue he pressured Ukraine for dirt on a political opponent using aid money as leverage.

A 'troubling' complaint

The House of Representatives voted 421-0 on Wednesday for a resolution calling on Trump to release the whistleblower's complaint to Congress, despite the administration letting them view the classified document at secure locations in the U.S. Capitol.

The Senate passed a similar resolution by unanimous voice vote on Tuesday, with Republicans joining Democrats in backing the release of the document.

After reading the report, lawmakers from both parties expressed concern about the contents. Republican Senator Ben Sasse said there were "really troubling things there" and Democratic minority leader Chuck Schumer said that after reading the complaint "I'm even more worried about what happened."

The New York Times reported on Wednesday evening that the whistleblower's complaint raised alarms not only about what the presidents said in the July 25 phone call, but also about how the White House handled records of the conversation. 

The newspaper also reported that the whistleblower identified multiple witnesses who could corroborate the complaint.

Pressure mounts on Trump

Trump and Zelenskiy appeared side by side in New York on the sidelines of the U.N. General Assembly on Wednesday as pressure mounted on the U.S. president.

Both denied impropriety in their call, with Ukraine's president telling reporters: "Nobody pushed me."

At a news conference later, Trump accused Democrats of launching the impeachment inquiry "because they can't beat us at the ballot."