House Intelligence Committee Chairman Adam Schiff warned of possible legal action Thursday if intelligence officials did not share a potentially explosive whistleblower complaint prompted by President Donald Trump’s interactions with a foreign leader.

Mr Schiff called acting director of national intelligence Joseph Maguire’s refusal to share the complaint with Congress “unprecedented” and said he understood the Justice Department was involved in the decision.

“We cannot get an answer to the question about whether the White House is also involved in preventing this information from coming to Congress,” Mr Schiff said, adding: “We’re determined to do everything we can to determine what this urgent concern is to make sure that the national security is protected.”

Someone, Adam Schiff said, “is trying to manipulate the system to keep information about an urgent matter from the Congress. ... There certainly are a lot of indications that it was someone at a higher pay grade than the director of national intelligence.”

Donald Trump has denied doing anything improper.

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Mr Schiff spoke following a closed-door appearance before committee members by Intelligence Community Inspector General Michael Atkinson, who reviewed the complaint and determined it was credible and troubling enough to be considered a matter of “urgent concern,” a legal threshold that requires notification of congressional oversight committees.

During the meeting, Mr Atkinson declined to provide any substantive detail about the whistleblower complaint, Mr Schiff indicated. The congressman said he does not know if reports by The Washington Post and other media outlets about its contents are accurate or not.

Mr Maguire’s refusal to share the complaint has touched off a legal and political dispute that has spilled into public view and prompted speculation that the spy chief may be improperly protecting the president.

“We are exploring with the House general counsel what our options are,” Mr Schiff said. “I would imagine if it comes down that we have to go to court to get this that we will have a very good case to seek a temporary restraining order or a mandamus or some urgent form of relief because the inspector general has said this cannot wait. ... There’s an urgency here that I think the courts will recognize.”

Mr Schiff said that Mr Maguire is scheduled to appear before his committee in a public session next week “where he can explain why this urgent concern should not be shared with the Congress.”

Adam Schiff spoke to reporters about two hours after Mr Trump disputed the report that his interaction with a foreign leader had prompted an official in the US intelligence community to file a whistleblower complaint, saying it was inconceivable that he would say anything inappropriate on a heavily monitored phone call.

“Virtually anytime I speak on the phone to a foreign leader, I understand that there may be many people listening from various US agencies, not to mention those from the other country itself,” Donald Trump wrote on Twitter. “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. I would only do what is right anyway, and only do good for the USA!”

Mr Trump dismissed the report as “Fake News” and said in another tweet that he was subject to “Presidential Harassment!”

President Trump’s interaction with the foreign leader included a “promise” that was regarded as so troubling that it prompted the intelligence official to file a whistleblower complaint with the inspector general for the intelligence community, according to two former U.S. officials familiar with the matter. The former officials spoke to The Post on the condition of anonymity because they were not authorised to discuss the matter publicly.

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One former official said the communication was a phone call.

It was not immediately clear which foreign leader Trump was speaking with or what he pledged to deliver, but his direct involvement in the matter had not been previously disclosed. It raises new questions about the president’s handling of sensitive information and may further strain his relationship with U.S. intelligence agencies.

The White House declined to comment late Wednesday night. The Office of the Director of National Intelligence and a lawyer representing the whistleblower declined to comment.