The FBI, working with the Pentagon, has confirmed that it opened an investigation into the leak of intelligence documents detailing Israel’s plans for a retaliatory strike following Iran’s ballistic missile attack on October 1. 

Although it hasn’t been determined whether the documents were leaked by an insider or exposed through a hack, the investigation is focusing on who had access to the documents, CNN reported on Tuesday, indicating that investigators, for the time being, could be approaching the security breach as an inside job.

“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 FBI said in a statement reported by multiple news outlets on Tuesday. “As this is an ongoing investigation, we have no further comment.” 

The classified documents first began circulating online last week after appearing on a Telegram channel called “Middle East Spectator,” — the channel’s X account indicates that it is based in Iran. The documents were attributed to the Geospatial Intelligence Agency and the National Security Agency and said that Israel was conducting munitions preparations and exercises to prepare for a likely strike against Iran.  

The incident has prompted renewed questions about Iran sympathizers in the Biden administration who have access to classified information and has risked straining America’s relationship with Israel.

On Monday, a national security council spokesman, John Kirby, said that President Biden is “deeply concerned” about the leak and that officials are working on learning “what happened here, learning how it happened, and preventing it from happening again,” as the Sun reported. He also said that authorities have no expectations that similar documents will be released to the public.