The CIA has violated the trust of the US President, according to an official who used to listen to Donald Trump's phone calls from the White House situation room.

Key points: The former executive secretary of the National Security Council says the reputation of the CIA could be hurt for "years to come"

The former executive secretary of the National Security Council says the reputation of the CIA could be hurt for "years to come" Presidential phone calls to foreign leaders are not recorded, but transcribed by three different officials

Presidential phone calls to foreign leaders are not recorded, but transcribed by three different officials The acting director of National Intelligence, Joesph Maguire, says the whistleblower "followed the law every step of the way"

An impeachment inquiry has been opened into Mr Trump after a whistleblower complaint alleged he put pressure on the President of Ukraine, Volodymyr Zelenskiy, to investigate Joe Biden, a domestic political rival of Mr Trump.

The US President's phone calls to foreign leaders are highly sensitive and details should never have been shared with the whistleblower according to Fred Fleitz, who served as the chief of staff and former executive secretary of the National Security Council between May and October last year.

"The CIA is trusted to basically serve as clerks in this vital capacity to write up these phone calls and to safeguard this information," he told The World Today.

"If they're letting this information get around, they've violated the trust of the President."

Whistleblower reportedly a CIA official

Mr Fleitz criticised the CIA, the foreign intelligence organisation of the United States, after a report in the New York Times revealed it was a CIA official who filed the complaint.

"I think that's going to hurt the reputation of the CIA, possibly for many years to come," said Mr Fleitz, who himself is a former CIA official.

The source of the complaint was not one of the CIA officers present and listening during the phone call between Mr Trump and Mr Zelenskiy, but according to the complaint, the whistleblower was told of concerns by those present during the call.

"This person was told about the call by one other person, maybe multiple people and that's a violation of how these calls are supposed to be handled," Mr Fleitz said.

"You're not supposed to discuss them with people not on the dissemination list."

Meanwhile, Adam Schiff, the ranking Democrat on Congress' House Intelligence Committee, has described the whistleblower's complaint as "very credible" and "deeply disturbing".

Since leaving the White House in October 2018, Mr Fleitz has become president of the Centre for Security Policy, which the Southern Poverty Law Centre has designated as an anti-Muslim hate group.

"The Centre for Security Policy has gone from a respected hawkish think tank focused on foreign affairs to a conspiracy-oriented mouthpiece for the growing anti-Muslim movement in the United States," according the Southern Poverty Law Centre.

How the President's phone calls are recorded

Mr Fleitz said he was frequently in the White House situation room during phone calls from Mr Trump to foreign leaders during his five-month tenure.

Fred Fleitz, right, with former National Security Advisor John Bolton, to whom he was chief of staff in the Trump White House. ( Supplied )

Part of his job was signing off on the transcripts of calls and controlling the flow of these records throughout the White House and to the US government officials who were approved to receive details of the calls.

"We don't do audio recordings of presidential phone calls," he said. "We haven't done that since Watergate."

"Instead there's probably three individuals, probably intelligence officers, who are making notes on the call and then afterwards they compare notes to put together what is very close to a verbatim transcript."

Whistleblower criticised

Mr Trump hit out at the whistleblower during a closed-door meeting with US State Department officials overnight.

The US President called the whistleblower "close to a spy" and reminisced about how spies were dealt with "in the old days", according to reports.

These sentiments were echoed by Mr Fleitz, who said he believed the whistleblower was not genuine and instead promoted the idea the complaint was part of a plot with Democrats on the House Intelligence Committee.

"I think it's a fake," he said.

There is no evidence the complaint is fake or that Democrats had any involvement in the submission of the complaint.

Acting director of National Intelligence Joesph Maguire, who was responsible for handling the complaint, said in front of the House Intelligence committee the whistleblower had "followed the law every step of the way".