FILE - House Intelligence Committee Chairman Adam Schiff, a Democrat, speaks during a hearing on Capitol Hill in Washington, July 24, 2019.
FILE - House Intelligence Committee Chairman Adam Schiff, a Democrat, speaks during a hearing on Capitol Hill in Washington, July 24, 2019.

VOA National Security Correspondent Jeff Seldin contributed to this report.

The U.S. House intelligence committee held a closed-door session Thursday with Intelligence Community Inspector General Michael Atkinson as lawmakers hoped to learn more details of a secret whistleblower complaint that has sparked a legal battle between lawmakers and the Trump administration.

Atkinson's testimony came as the Washington Post reported the complaint involves communications between President Donald Trump and a foreign leader that involved a "promise."

The Post said its report was based on two former U.S. officials familiar with the matter, but that it was not clear which leader was in communication with Trump or what the U.S. leader may have promised.

Congressman Adam Schiff, who chairs the committee, said Atkinson determined the whistleblower complaint was "both credible and urgent," meaning under law it has to be reported to Congress.

"The Committee places the highest importance on the protection of whistleblowers and their complaints to Congress," Schiff said in a statement.

Acting Director of National Intelligence Joseph Maguire has so far refused to provide details of the complaint to lawmakers.

A lawyer for Maguire's office said the allegation in the complaint does not meet the "urgent concern" standard.

Schiff said Maguire will make his own appearance before the committee for public testimony Sept. 26.

Senator Mark Warner said Thursday he and Senate Intelligence Committee Chairman Richard Burr "have made it very clear" that they expect Maguire and Atkinson to come before the committee and "clear this issue up."

"You cannot end up with some circumstance where you have got a whistleblower muzzled."