A whistleblower complaint about conversations between President Donald Trump and a foreign leader involves Ukraine, according to The Washington Post and The New York Times.

The complaint centers on a "promise" Trump made to the foreign leader, The Post said, citing two former US officials.

The complaint shocked the intelligence community. A former CIA official described it to Business Insider as a "DEFCON 1" situation.

About 2 1/2 weeks before the complaint was filed, Trump spoke on the phone with Ukraine's new president, Volodymyr Zelensky.

That phone call was already the focus of an investigation by House Democrats, who want to know whether Trump and his attorney Rudy Giuliani pressured Ukraine to investigate Joe Biden's son.

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A whistleblower's complaint about President Donald Trump at the center of a battle between the director of national intelligence and Congress partly involves Ukraine, The Washington Post reported Thursday.

Two former US officials with knowledge of the matter told The Post that the complaint involved conversations with a foreign leader and a "promise" made by Trump. At least part of the whistleblower's complaint involves Ukraine, The Post reported and The New York Times later confirmed.

The inspector general of the intelligence community decided the complaint was serious enough to warrant alerting Congress. However, the acting director of national intelligence, Joseph Maguire, has declined to provide the original complaint to members of Congress, citing advice from the Department of Justice.

Few specifics are known about the complaint, but here is what has been reported:

The complaint was made on August 12.

It came from an unnamed whistleblower, identified as a US intelligence official who had worked at the White House.

The whistleblower alerted the inspector general of the intelligence community, an internal federal watchdog.

The complaint was prompted by conversations between Trump and a foreign leader, according to several outlets.

According to The Post, a "promise" was made by Trump. No specifics have been made public.

According to The Post and The Times, the complaint involves Ukraine, though it's unclear how.

The complaint did not stem from a single conversation, according to a Post report of remarks by the inspector general at a closed-door House Intelligence Committee hearing on Thursday.

The White House did not immediately respond to a request for comment from Business Insider.

Former intelligence officials have told Business Insider that the situation is unprecedented. One former CIA official described it as "equivalent to an imminent threat" and as a "DEFCON 1" situation.

Trump has denied doing anything wrong.

"Virtually anytime I speak on the phone to a foreign leader, I understand that there may be many people listening from various U.S. agencies, not to mention those from the other country itself," he tweeted Thursday.

He added: "Knowing all of this, is anybody dumb enough to believe that I would say something inappropriate with a foreign leader while on such a potentially 'heavily populated' call."

About 2 1/2 weeks before the whistleblower's complaint was registered, Trump spoke on the phone with Ukraine's new president, Volodymyr Zelensky, a former TV comedian and political newcomer who was elected in May.

There is no readout of the call on the White House's website, but the Ukrainian president's office said in a July 25 readout that Trump "is convinced that the new Ukrainian government will be able to quickly improve image of Ukraine, complete investigation of corruption cases, which inhibited the interaction between Ukraine and the USA."

In a call with Russian President Vladimir Putin on July 31, Trump offered US help to extinguish wildfires in Siberia, and the two discussed restoring "full-scale bilateral relations" between the US and Russia, the Kremlin said in a statement.

It is not clear whether either of those calls or other conversations prompted the complaint.

Separately from the intelligence-community complaint, House Democrats are investigating the call with Zelensky. They want to know whether Trump and his personal attorney Rudy Giuliani attempted to pressure Ukrainian authorities to investigate the son of Joe Biden, a 2020 Democratic presidential candidate.

Of the complaint about Trump's communications with the foreign leader, Giuliani told The Post that he was "not even aware of the fact that he had such a phone call," adding, "If I'm not worried about it, he's not worried about it."