U.S. Secretary of Defense Lloyd Austin briefed reporters on the leaking of dozens of sensitive and highly classified documents Tuesday, saying they were "somewhere in the web."
"Well, they were somewhere…in the web and where exactly and who had access at that point, we don't know. We simply don't know at this point," Austin said.
Fox News learned earlier Tuesday through conversations with a variety of American defense and intelligence officials that as many as 53 documents were posted online, which were dated between Feb. 23 and March 1.
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The documents, officials told Fox News, may have come from outside the Pentagon.
Austin addressed the leak at the beginning of a news conference with Secretary of State Antony Blinken, Philippine Secretary of Foreign Affairs Enrique Manalo and Philippine Officer in Charge of the Department of National Defense Carlito Galvez, regarding the additional sites being established on the island nation to help facilitate training opportunities and improve disaster response.
Austin told reporters he was first briefed about the unauthorized disclosure of sensitive and classified material on the morning of April 6.
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"Since then, I’ve been convening with senior department leaders daily on our response, and I’ve directed an urgent cross department effort," he said. "We’ve referred the matter to the Department of Justice (DOD), which has opened a criminal investigation."
One reporter asked him how he was only just made aware of the documents a week ago when leaked classified documents from the Pentagon had been posted online for months.
Austin told the reporter the documents his department was aware of were dated Feb. 28 and March 1, adding that he did not know if there are other documents that were online before those dates.
"These are things that we will find out as we continue to investigate," he said. "We take this very seriously and will continue to investigate and turn over every rock until we find the source of this and the extent of it."
Austin said he could not say much more about the leaked documents because of the open investigation.
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"Nothing will ever stop us from keeping America secure," Austin said.
The Department of Defense did not immediately respond to questions regarding the timeline of the leak and why Austin was notified of the leak weeks after allegedly being posted.
The briefings from the DOD are typically distributed to anywhere between 1,000 and 5,000 people with necessary security clearances and include details on the war in Ukraine and battlefield assessments.
DOD briefings are also delivered electronically on secure iPads, and if printed out, investigators can track where they were printed from because they must run through secure printers that are often numbered.
Fox News learned that within the classified documents published online, there is intelligence that was not part of the DOD briefing books that appears to be produced by agencies like the Central Intelligence Agency and National Security Agency.
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.
Greg Norman and Jennifer Griffin of Fox News contributed to this report.