The Department of Defense is investigating how U.S. intelligence documents detailing Israeli plans to attack Iran were leaked and published in an online forum, the White House said on Monday.

“We’re not exactly sure of how these documents found their way into the public domain,” said White House national security spokesperson John Kirby. “I know the Department of Defense is investigating this, and I’m sure that as they work through that, they’ll try to determine the manner in which they did become public.” 

The White House does not yet know if the documents were purposely leaked by an official who had access to them or whether they were obtained as the result of a hack, according to Kirby.

President Joe Biden will be updated on the progress of the investigation and “any mitigation measures and recommendations that come as a result of the investigative efforts, [and] how to prevent it from happening again,” Kirby told reporters. “The president remains deeply concerned about any leakage of classified information into the public domain. That is not supposed to happen, and it’s unacceptable when it does.” 

The reportedly top secret documents were published last week in a Telegram channel called “Middle East Spectator” that is believed to be affiliated with Iran, although it is operated anonymously. An account in the channel claimed the documents came from the National Geospatial-Intelligence Agency, headquartered at the Defense Department.

The authenticity of the documents has not been verified. Kirby did not refute their authenticity during his Monday remarks to the media.

Several U.S. lawmakers, including House Speaker Mike Johnson (R-LA), have called for investigations into the source of the leak.