The FBI is investigating secret document leaks about Israel's planned attack on Iran

The FBI is investigating the leak of classified documents that contained top-secret U.S. intelligence on Israel's planned attack on Iran, Fox News Digital confirmed.

“The FBI is investigating the suspected loss of classified documents and is working closely with our partners in the Departments of Defense and Intelligence,” the FBI said in a statement. “As this is an ongoing investigation, we have no further comment.”

The Ministry of Defense has already confirmed that it is investigating the unauthorized release.

White House National Security Council spokesman John Kirby told reporters on Monday he had no information about whether the unauthorized release was the result of a hacker attack or an employee leak.

The US is investigating the release of confidential documents relating to Israel's planned attack on Iran

“We are not entirely sure how these documents came into the public domain. I know the Department of Defense is looking into this,” Kirby said. “I just can't answer your question about whether it was a leak or a hacker attack. At this point we will allow the investigation to follow its logical course.”

The Ministry of Defense has already confirmed that it is investigating the unauthorized release. (Daniel Slim/AFP via Getty Images)

“We are deeply concerned, and the president remains deeply concerned, about the release of classified information to the public,” Kirby said. “This shouldn’t happen. And it’s unacceptable when it happens.”

Kirby said he had no indication that additional classified documents would become public and that the U.S. had communicated with Israeli counterparts about the disclosure.

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The FBI confirmed an investigation into the alleged leak of classified documents. (AP Photo/Charlie Neibergall, File)

“I will let the Israelis discuss whether, what, how and when they decide to take additional military action in response to the Iranian attack on October 1,” Kirby said. “So they can really talk.”

The documents, classified top secret, were posted on the messaging app Telegram last week.

The documents were attributed to and referenced by the US Geospatial Intelligence Agency and the National Security Agency Israel was still moving The documents were shareable within the “Five Eyes”, consisting of the USA, Great Britain, Canada, New Zealand and Australia.

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This is a developing story. Check back for updates.

The Associated Press contributed to this report.