Acting director of national intelligence Joseph Maguire is set to speak publicly for the first time about a secret whistleblower complaint involving US President Donald Trump.

Democrats in the House of Representatives who have read the document have said it is “deeply disturbing”.

House Democrats who are now mulling Mr Trump’s impeachment are hoping that Mr Maguire will explain why he withheld the intelligence community whistleblower’s complaint from Congress for weeks.

Mr Maguire will then go behind closed doors to speak to the Senate intelligence panel.

There were signs that the document, now at the centre of a firestorm about Mr Trump’s handling of Ukraine, could be made public as soon as Thursday.

Shortly before midnight on Wednesday, Utah Representative Chris Stewart, a Republican member of the House intelligence committee, tweeted: “BREAKING NEWS: The whistleblower complaint has been declassified. I encourage you all to read it.”

New York Representative Hakeem Jeffries, a member of the Democratic leadership, said on Wednesday evening that he expects the complaint would be made public “sooner rather than later”.

The document was made available to members of House and Senate intelligence committees on Wednesday after Mr Maguire had initially determined they could not see it.

The complaint is at least in part related to a July phone call between Mr Trump and Ukrainian President Volodymyr Zelenskiy in which Mr Trump prodded Mr Zelenskiy to investigate Democratic political rival Joe Biden.

Ukrainian President Volodymyr Zelenskiy with Donald Trump at the InterContinental Barclay New York hotel during the United Nations General Assembly
Volodymyr Zelenskiy with Donald Trump at the InterContinental Barclay New York hotel during the UN General Assembly (Evan Vucci/AP)

The White House released a rough transcript of that call on Wednesday morning.

House Democrats emerging from a secure room would not divulge details of the classified document but described it as disturbing and urgent.

House intelligence committee chairman Adam Schiff said it “exposed serious wrongdoing” and “certainly provides information for the committee to follow up with others”.

The complaint showed the whistleblower learned details of the call from White House officials, according to one person familiar with the complaint who was granted anonymity to discuss it.

Another such person said the politicians did not learn the identity of the whistleblower.

House Speaker Nancy Pelosi – who on Tuesday fully endorsed an impeachment investigation in light of the Ukraine revelations – and Senate Democratic Leader Chuck Schumer also viewed the complaint.

Mr Schumer said he was even “more worried” now than he was before reading it and “there are huge numbers of facts crying out for investigation”.

Mr Trump, whose administration had earlier baulked at turning over the complaint, said on Wednesday afternoon that “I fully support transparency on the so-called whistleblower information” and that he had communicated that position to House minority leader Kevin McCarthy.

The rough transcript released by the White House on Wednesday showed that Mr Trump prodded Mr Zelenskiy to work with the US attorney general and Mr Trump’s personal lawyer Rudy Giuliani to investigate Mr Biden.

Mr Zelenskiy said his comments in the conversation with Mr Trump should not have been publicly released, and he played down Ukraine’s investigation of Mr Biden, a former vice president who is now a 2020 presidential candidate.

Politicians said they needed to see the complaint, not just the memo about the call, as they investigate the president and whether his actions were inappropriate.

Ms Pelosi on Tuesday said that if Mr Trump abused his presidential powers, it would mark a “betrayal of his oath of office”.

Nancy Pelosi
Nancy Pelosi (Susan Walsh/AP)

The unidentified whistleblower first submitted a complaint to Michael Atkinson, the US government’s intelligence inspector general, in August.

Mr Maguire then blocked release of the complaint to Congress, citing issues of presidential privilege and saying the complaint did not deal with an “urgent concern”.

Mr Atkinson disagreed, but said his hands were tied.

Mr Atkinson, who met privately with House politicians last week, will talk behind closed doors to the Senate intelligence panel on Thursday.

The House and Senate committees have also invited the whistleblower to give evidence, but it is uncertain whether the person will appear and whether his or her identity could be adequately protected without Mr Maguire’s blessing.

The whistleblower is prepared to speak privately before the Senate and House intelligence committees but the person’s lawyers want to first ensure that they have the appropriate security clearances so that they can be present for any meeting, according to correspondence reviewed by the Associated Press.