The National Archives and Records Administration confirmed Friday that items marked "classified" were among the 15 boxes of White House records retrieved from former President Donald Trump's home.
The National Archives noted that the Trump administration did not fully capture all of the social media posts made by the ex-president and his staff.
The House Oversight and Reform Committee received two letters from the U.S. Archivist.
The Archives has identified items marked as classified national security information within the boxes.
The discovery of those classified documents in Trump's Palm Beach, Florida, home prompted NARA staff to reach out to the Department of Justice.
The National Archives should have received all 15 boxes directly from the White House after Trump left office, as required by law, according to the agency.
As soon as the president leaves office, all applicable materials, such as documents, photos, correspondence and pamphlets, must be preserved and transferred to the National Archives.
The Archives has identified certain social media records that were not captured and preserved by the Trump Administration, and that some White House staff conducted official business using non-traditional methods.
A spokeswoman for Trump didn't respond to CNBC's request for comment.
Past presidents have had to return items that were taken after leaving the White House because of Presidential Records Act violations. The Washington Post has reported that the volume of records removed from Mar-a-Lago is atypical.
Former White House officials have recently shed light on Trump's habit of ripping up documents.
The Post reported that the boxes included a letter to Trump from Obama, as well as Trump's own.
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