WASHINGTON (AP) — The government's intelligence watchdog is set to testify Thursday in a closed session before the House intelligence committee about the handling of a whistleblower complaint.

The Washington Post reported the complaint involves an intelligence official's allegation that President Donald Trump made an unspecified "promise" to an unidentified foreign leader. The Post cited two anonymous former U.S. officials.

The Associated Press has not confirmed the report.

Intelligence Committee Chairman Rep. Adam Schiff, D-Calif., says inspector general Michael Atkinson determined the whistleblower complaint was "credible and urgent" and should be "transmitted to Congress."

Atkinson is scheduled to testify Thursday.

The White House had no immediate comment.

Joseph Maguire, acting director of national intelligence, has refused to discuss details. He is expected to testify publicly about the whistleblower complaint on Sept. 26.

Schiff subpoenaed Maguire, saying he was withholding a whistleblower complaint from Congress and questioning whether he had been directed to do so by the White House or the attorney general.

Schiff did not divulge the subject of the complaint, but said the committee "places the highest importance on the protection of whistleblowers and their complaints to Congress."

In a letter Tuesday, the general counsel for the Office of the Director of National Intelligence, Jason Klitenic, wrote that the agency is protecting the whistleblower and argued the allegation does not meet the definition of "urgent concern." He said the complaint "concerned conduct from someone outside the intelligence community and did not relate to 'intelligence activity' under the DNI's supervision."

Schiff said last week that Maguire is required to share the complaint with Congress and said the attempt to hold it back "raises serious concerns about whether White House, Department of Justice or other executive branch officials are trying to prevent a legitimate whistleblower complaint from reaching its intended recipient, the Congress, in order to cover up serious misconduct."