The United States is investigating the unauthorized release of classified documents detailing Israel's planned attack against Iran, The Associated Press reported.

The documents, attributed to the U.S. Geospatial Intelligence Agency and National Security Agency, note that Israel was still moving military assets in place to conduct a military strike in response to Iran's blistering ballistic missile attack on Oct. 1. They were sharable within the "Five Eyes," which are the U.S., Great Britain, Canada, New Zealand and Australia.

The documents, which are marked top secret, were posted to the Telegram messaging app last week and first reported by CNN and Axios. The AP first reported Sunday about the U.S. investigation into the unauthorized release, citing three U.S. officials. The AP said a fourth U.S. official, who also spoke on condition of anonymity, indicated that the documents appeared to be legitimate. 

House Speaker Mike Johnson, R-La., also confirmed the investigation in an appearance on CNN. 

"The leak is very concerning. There's some serious allegations being made, there's an investigation underway, and I'll get a briefing on that in a couple of hours," Johnson said Sunday on CNN's "State of the Union." "There's a classified level briefing and then another. But we're following it closely." 

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Aerial view of the Pentagon on March 31, 2024. (Daniel Slim/AFP via Getty Images)

The investigation is also examining how the documents were obtained – including whether it was an intentional leak by a member of the U.S. intelligence community or by another method, like a hack – and whether any other intelligence information was compromised, one of the officials told the AP, adding that officials are working to determine who had access to the documents before they were posted. 

The documents first appeared online Friday via a channel on Telegram, claiming they had been leaked by someone in the U.S. intelligence community, then later the U.S. Defense Department. The information appeared entirely gathered through the use of satellite image analysis.

President Biden talks with Israeli Prime Minister Benjamin Netanyahu in the Oval Office of the White House, July 25, 2024. (AP Photo/Susan Walsh, File)

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The AP reported that one of the two documents resembled the style of other material from the U.S. National Geospatial Intelligence Agency leaked by Jack Teixeira, an Air National Guardsman who pleaded guilty in March to leaking highly classified military documents about Russia’s war on Ukraine and other national security secrets.

The Telegram channel involved in the leak identifies itself as being based in Tehran, Iran's capital. It previously published memes featuring Iran’s supreme leader, Ayatollah Ali Khamenei, and material in support of Tehran’s self-described "Axis of Resistance," which includes Middle East terrorist groups armed by the Islamic republic.

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In a statement to the AP, the Pentagon said it was aware of the reports of the documents but did not elaborate further. The AP said the Israeli military did not immediately return their request for comment.

Fox News Digital reached out to the U.S. Department of Defense but did not immediately hear back. 

The Associated Press contributed to this report.