The FBI is conducting a high-level investigation into the leak of two highly classified U.S. intelligence documents detailing Israeli military preparations for a retaliatory strike on Iran. The leak, which surfaced on the Telegram messaging platform last week, has alarmed U.S. officials at a time of heightened tensions between Israel and Iran, as well as growing regional instability. The documents, marked as top-secret, appear to have been prepared by the National Geospatial-Intelligence Agency (NGA) and the National Security Agency (NSA), based on satellite imagery and intelligence from mid-October.

The breach, which the FBI suspects may have come from a government insider, is being treated with the utmost seriousness, given its potential to strain U.S.-Israel relations. "The FBI is investigating the alleged leak of classified documents and working closely with our partners in the Department of Defense and Intelligence Community," the bureau said in a statement on Tuesday. While no conclusions have been drawn, U.S. officials familiar with the matter noted that at least one of the documents appears to have been scanned from a printed briefing book, potentially narrowing the pool of those responsible.

The leaked documents detail Israeli preparations for a military response to a missile barrage from Iran on October 1, the second such attack in the past six months. The documents include assessments of Israeli Air Force exercises involving fighter jets and air-to-surface missiles, as well as the movement of advanced munitions in preparation for a strike on Iranian targets. Israel has recently intensified its military operations in Gaza and Lebanon following the death of Hamas leader Yahya Sinwar, further raising concerns of a broader conflict with Iran.

White House spokesman John Kirby said on Monday that U.S. officials are still working to determine whether the leak resulted from a hack or an internal breach. "We're not exactly sure how these documents found their way into the public domain," Kirby said. "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 documents were first shared by an account called "Middle East Spectator," which posted them on Telegram. The account has denied any direct connection to the source of the documents, speculating that the leak may have originated from a whistleblower within the U.S. Department of Defense. A U.S. official said that while the content of the documents is not necessarily surprising to those familiar with U.S. surveillance of its allies, the fact that they were made public poses a significant risk to relations with Israel.

The FBI's investigation is focused on identifying who had access to the documents and how they were leaked. Given the sensitive nature of the documents, officials say the pool of individuals who printed or handled the material is relatively small. Investigators are working with Pentagon officials and intelligence agencies to trace the chain of custody and determine whether the breach could have come from within the U.S. government.

The leak comes at a particularly precarious moment for U.S.-Israel relations, as the Biden administration navigates a complex web of conflicts in the Middle East, including Israel's military operations in Gaza and Lebanon, and the broader threat of escalation with Iran. Any public disclosure of U.S. surveillance of Israeli military activities risks undermining trust between the two nations.

The leaked documents are marked for distribution only to the U.S. and its "Five Eyes" allies-Australia, Canada, New Zealand, and the United Kingdom. They include detailed intelligence on Israeli military activities, such as air force exercises and munitions movements, reportedly in preparation for a retaliatory strike on Iran. While U.S. officials acknowledge that surveillance of allies is a standard practice, having such information leak publicly could severely damage diplomatic efforts, particularly as the U.S. attempts to defuse the multiple conflicts in which Israel is currently embroiled.

Former President Donald Trump weighed in on the matter on Tuesday, calling the leaks "devastating" for Israel and speculating that the breach might have originated within the U.S. Department of Defense. In a post on Truth Social, Trump wrote, "Israel has been seriously damaged and compromised by this. Wartime strategy and data. Probably came from Defense Department. MUST FIND THE LEAKER!"

The leak has revived concerns over the security of classified U.S. intelligence, echoing a similar breach last year when Air National Guardsman Jack Teixeira leaked sensitive military information on Discord. That leak strained U.S. relations with key allies and led the Pentagon to tighten access to classified materials. Teixeira, who was sentenced to 16 years in prison, left an electronic trail that allowed investigators to quickly identify him. This latest breach, however, is expected to be more difficult to trace, given that the documents appear to have been scanned and shared anonymously.