President Biden is "deeply concerned" about the unauthorized release of classified documents on Israel's preparation for a potential retaliatory attack on Iran, a White House spokesman said Monday. The Biden administration is still not certain if the classified information was leaked or hacked, White House national security spokesman John Kirby said. Officials don't have any indication at this point of "additional documents like this finding their way into the public domain," he said, per the .

Kirby added that the Pentagon is investigating. US officials on Saturday had confirmed an investigation by the administration. "We're deeply concerned, and 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," Kirby said. The documents note that Israel was still moving military assets in place to conduct a military strike in response to Iran's blistering on Oct. 1.

They were sharable within the "Five Eyes," an intelligence alliance comprised of the US, Britain, Canada, New Zealand, and Australia. Marked top secret, the documents first appeared online Friday on the Telegram messaging app and quickly spread among Telegram channels popular with Iranians, per the AP. Analysts at the SITE Intelligence Group, a consultancy that monitors and analyzes online threats from extremist groups, tracked the release of the documents to a Telegram channel popular with Iran-backed mi.