US investigating leak of highly classified intelligence about Israel’s plans to attack Iran, sources say

(CNN)- The United States is investigating the leak of highly classified US intelligence information about Israel’s plans to retaliate against Iran, according to three people familiar with the matter. One of the people familiar confirmed the authenticity of the documents.

An American official told CNN that this leak is extremely worrying.

The documents, dated October 15 and 16, began circulating online this Friday after being posted on Telegram by an account called “Middle East Spectator.”

They are marked top secret and have markings indicating that they are to be seen only by the United States and its “Five Eyes” allies: Australia, Canada, New Zealand, and the United Kingdom.

They describe the preparations Israel is making for an attack on Iran. One of the documents, which it says was compiled by the National Geospatial-Intelligence Agency, indicates that plans include moving munitions to Israel.

Another document says its source is the National Security Agency and details Israeli Air Force exercises involving air-to-surface missiles, also seen as preparation for an attack on Iran. CNN is not directly quoting or displaying the documents.

A US official said the investigation was examining who had access to the alleged Pentagon document. Any such leak would automatically trigger an investigation by the Pentagon and US intelligence agencies as well as the FBI. The FBI declined to comment.

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The leak comes at a highly sensitive time in US-Israel relations and is sure to anger the Israelis, who are preparing to attack Iran in retaliation for the Iranian missile bombing on October 1. One of the documents also suggests something Israel has always refused to publicly confirm: that the country has nuclear weapons. The document said the US has seen no indication that Israel plans to use nuclear weapons against Iran.

Mick Mulroy, former deputy assistant secretary of defense for the Middle East and retired CIA officer, said, “If it is true that Israeli strategic plans for responding to the October 1 Iranian attack have been leaked, then that is a serious breach.”

Mulroy said that “future coordination between the US and Israel could also be challenged. Trust is a vital component in a relationship, and depending on how it’s leaked, that trust can be eroded.

The National Security Council referred CNN to the Office of the Director of National Intelligence and the Pentagon for comment. The Pentagon and the National Geospatial-Intelligence Agency declined to comment. CNN has contacted the National Security Agency for comment.

“Both of these documents are bad, but not terrible,” another US official said. The concern is whether there are more.”

It is unclear how the documents became public, nor is it clear whether they were hacked or intentionally leaked. The United States is already on high alert for Iranian hacking campaigns; American intelligence agencies said in August that Iran had hacked documents related to Donald Trump’s campaign.

Axios first reported the leaked documents on Saturday.

A major US intelligence leak last year strained US relations with allies and partners including South Korea and Ukraine after a 21-year-old Air National Guard member posted highly classified information on a networking platform.

CNN’s Evan Perez and Katie Bo Lillis contributed to this report