John Kirby
John KirbyREUTERS/Jim Bourg

US President Joe Biden is “deeply concerned” following the leak of highly classified US intelligence on Israel’s plans to attack Iran and will be “actively monitoring” the investigation, national security spokesperson John Kirby said on Monday.

“We’re deeply concerned, and the President remains deeply concerned about any leakage of classified information into the public domain. That, that is not supposed to happen, and it’s unacceptable when it does,” Kirby told reporters.

“You can rest assured that he will be actively monitoring the progress of the investigative effort to figure out how this happened, and obviously he’ll be very interested in hearing any mitigation measures and recommendations that come as a result of the investigative efforts,” he stressed

Kirby added that it is not yet known how the documents were released and that the Department of Defense is continuing their investigation.

Kirby also said that “at this time” they have no reason to believe similar documents will be released.

“We don’t have any indication at this point that there’s an expectation that there will be additional documents like this finding their way into the public domain,” he added.

The documents, dated October 15-16, began circulating this past Friday after an Iran-affiliated account named, "The Middle East Spectator," posted them on Telegram.

The documents describe Israel's preparations for a strike against Iran, and were marked top secret and were intended to be seen only by the US and its "Five Eyes" allies: Australia, Canada, New Zealand, and the UK, reported CNN.

One of the documents, which appears to have been compiled by the National Geospatial-Intelligence Agency, says the plans "involve Israel moving munitions around." Another document sourced to the National Security Agency outlines IAF exercises involving air-to-surface missiles.

US House Speaker Mike Johnson on Sunday expressed deep concern over the leak of the classified documents.

“The leak is very concerning. There’s some serious allegations being made there, an investigation underway, and I’ll get a briefing on that in a couple of hours,” Johnson told CNN. “We’re following it closely.”