The leak of dozens of U.S. documents containing in some cases what the Department of Defense is describing as "sensitive and highly-classified material" may have come from outside the Pentagon, Fox News has learned, based on conversations with a variety of American defense and intelligence officials.
As of Tuesday, 53 documents have been posted online, many of which are dated to Feb. 23 and March 1.
The Department of Defense briefings – which typically are distributed between 1,000 to 5,000 people with the appropriate security clearances, include details on the war in Ukraine and battlefield assessments, and usually are delivered electronically on secure iPads.
If those documents are printed out, investigators can track where they were printed from as the pages have to run through secure printers that are often numbered.
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Separately, among the classified documents published online, there is also highly classified intelligence that was not part of any of the Department of Defense briefing books, Fox News has learned.
That intelligence appears to be produced by other U.S. agencies like the Central Intelligence Agency and the National Security Agency.
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This intelligence is not easily accessed by those in the Pentagon and their inclusion suggests that the leak may have come from outside the Pentagon.
On Monday, Chris Meagher, assistant to the secretary of defense for public affairs said the Department of Defense is working "around the clock to look at the scope and scale of the distribution, the assessed impact and our mitigation measures" following the disclosure of the documents to the public.
"The Department of Defense's highest priority is the defense of our nation and our national security. We're not going to get into the validity of the purported documents posted online, but a Pentagon team continues to review and assess the veracity of the photographed documents that are circulating on social media sites and that appear in some cases to contain sensitive and highly-classified material," he said.
"These photos appear to show documents similar in format to those used to provide daily updates to our senior leaders on Ukraine and Russia-related operations, as well as other intelligence updates. Some of these images appear to have been altered," Meagher added. "We've been in close touch with the White House and with interagency partners on this issue, and an interagency effort has been set up with a focus on assessing the impact these photographed documents could potentially have on U.S. national security and on our allies and partners.
Milancy Harris, the deputy under secretary of defense for intelligence and security, is leading the Pentagon's internal investigation, coordinating with the DOD's office of Intelligence and Security, Public Affairs, Office of General Council, Legislative Affairs and the Joint Staff.
A defense official said each agency will have their own point person for the investigation, and that there is not yet any one person leading a whole interagency effort.
Fox News' Liz Friden contributed to this report.
