FBI investigating leak of classified docs on Israeli preparations for possible Iran strike

"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. "As this is an ongoing investigation, we have no further comment." 

White House National Security Council spokesman John Kirby told reporters on Monday that he did not have information on whether the unauthorized release was a result of a hack or an employee leak. 

"We're deeply concerned, and the president remains deeply concerned about any leakage of classified information into the public domain," Kirby said. "That is not supposed to happen. And it's unacceptable when it does." 

Kirby said he did not have any indication that additional classified documents would find their way into the public domain and that the U.S. has been in communication with Israeli counterparts about the disclosure.

"I'll let the Israelis speak to if, what, how and when they decide to take additional military action in response to Iran's Oct. 1 attack," Kirby said. "That's really for them to speak to." 

The documents are descriptions of satellite images showing Israeli warplanes preparing for a strike and practicing air refueling, according to officials. There is no information in the leaked documents about what the targets are or what Israeli plans to strike.

"These are NOT Israeli war plans for Iran," a senior U.S. defense official told Fox News.

The documents, which are marked top secret, were posted to the Telegram messaging app last week. 

Fox News' Jennifer Griffin and The Associated Press contributed to this report.