The US has launched an investigation into the leak of classified Pentagon documents detailing Israel’s preparations for a potential military strike against Iran, according to three sources familiar with the matter. One of the sources confirmed to CNN that the leaked documents are authentic.

The documents, dated October 15 and 16, outline Israeli military exercises and preparations for a long-range attack in response to Iran’s October 1 ballistic missile barrage. The documents, which surfaced on Telegram and were later posted online, were shared within the US-led “Five Eyes” intelligence alliance and attributed to the US Geospatial Intelligence Agency and National Security Agency.

The leaked files describe Israeli Air Force drills, including the use of air-launched ballistic missiles and covert drone activity. They also mention aerial refueling exercises and note Israel’s apparent ability to deploy unmanned aerial vehicles (UAVs) for intelligence gathering in Iran.

An investigation involving the FBI and Pentagon is underway to determine how the documents were accessed and leaked. Speculation has arisen that the leak could have been intentional, possibly aimed at deflecting criticism of the Biden administration’s influence on Israel.

The leak also coincides with recent statements by US President Joe Biden, who noted in Berlin that he had knowledge of how and when Israel would respond to the missile attacks from Iran.

The leak has caused concern among US officials, with one source describing it as “very worrying.”