President Joe Biden is “deeply concerned” about the release of classified documents about Israel’s preparation for possible retaliation against Iran, according to a White House spokesman.

US officials confirmed Saturday that the administration is investigating an unauthorized release of classified documents assessing Israel’s plans to attack Iran.

White House National Security Press Secretary John Kirby said Monday that the administration is still unsure whether the classified information that was publicly disclosed was leaked or the result of a system breach.

Kirby added that administration officials have no indication that “additional documents like these have been leaked.” He added that the Pentagon is investigating the matter.

“We are deeply concerned and the president remains deeply concerned about any leakage of classified information into the public sphere. That’s not supposed to happen, and it’s unacceptable when it does,” Kirby said.

The documents, attributed to the National Geospatial Intelligence Agency and the National Security Agency, said Israel was moving military assets to carry out a military strike in response to Iran’s Oct. 1 ballistic missile attack. The release of the documents was only for an intelligence alliance, the “Five Eyes”, made up of the US, Great Britain, Canada, New Zealand and Australia.

Classified as top secret, the documents first appeared online on Friday on the Telegram messaging app and quickly circulated on Telegram channels popular with Iranians.

Analysts at SITE Intelligence Group tracked the release of the documents on a Telegram channel popular with Iranian-backed militias. The channel contained posts from an anonymous user with a long history of posting other allegedly top secret content, who said he had access to the documents. The user also wrote that he had sold some of the hardware and also provided it to the Iranian military.