The FBI on Tuesday announced that it is investigating the unauthorized release of classified documents detailing Israel's potential retaliatory strike plans against Iran.
On Saturday, Axios reported that two alleged U.S. intelligence documents with details of Israeli preparations to hit back at Iran appeared on a Tehran-affiliated channel on messaging app Telegram. The channel's administrators said in a statement on Sunday that it was not linked to Iran but run by a "tight-knit team of fully independent journalists."
The documents were marked "top secret" and dated October 15 to 16. The documents purport to show "key munitions preparations and covert UAV [uncrewed aerial vehicle] activity" and were described as being linked to a possible Israeli attack on Iran.
The Associated Press (AP) previously reported that U.S. government officials were investigating the unauthorized release before the FBI confirmed the investigation on Tuesday.
In a statement provided to the AP, the FBI said it is "working closely with our partners in the Department of Defense and Intelligence Community." The agency offered no further comment.
On Monday, White House national security spokesman John Kirby spoke about the documents during a press briefing, stating that it remains unclear whether the information was leaked or obtained through hacking.
He added that officials don't have any indication at this point of "additional documents like this finding their way into the public domain."
"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 that were posted to Telegram are attributed to the National Geospatial-Intelligence Agency and the National Security Agency. The information was shareable among members of the Five Eyes intelligence alliance—which is made up of the U.S., the United Kingdom, Canada, Australia and New Zealand.
The documents outlined Israel's strategic military movements in preparation for a strike that's believed to be in response to Iran's ballistic missile attack on October 1st.
During that assault, Tehran launched its largest-ever missile attack on Israel, which appeared to have been mostly thwarted by Israeli defenses with the help of the United States and its allies.
Israel's military said Iran launched around 180 missiles toward Israel, with footage on Israeli TV appearing to show some of the weapons flying over the Tel Aviv area shortly before 7:45 p.m. local time on October 1. A senior Iranian official told Reuters that Supreme Leader Ayatollah Ali Khamenei gave the order for the attack.
This article includes reporting from The Associated Press.