US President Joe Biden speaks to the press following the 10th North American Leaders Summit, at the National Palace in Mexico City, on January 10, 2023. AFP
"I was surprised to learn there were any government records that were taken there to that office," Biden told reporters in Mexico City where he had a trilateral summit with the leaders of Mexico and Canada.
Biden said he doesn't know "what's in the documents" that were found in a locked closet when his attorneys were vacating office space at the Penn Biden Center in Washington, D.C.
The Penn Biden Center is a think tank not far from the White House, affiliated with the University of Pennsylvania and named for Biden, a veteran Democrat who served as US vice president from January 2009 to January 2017.
White House special counsel Richard Sauber issued a statement on Monday, saying that Biden periodically used this space from mid-2017 until the start of his 2020 presidential campaign.
This discovery of "what appears to be Obama-Biden Administration records, including a small number of documents with classified markings" was made in early November of 2022, according to the statement.
"They found some documents in a box in a locked cabinet, or at least a closet. And as soon as they did, they realized there were several classified documents in that box," Biden said on Tuesday.
The attorneys "did what they should have done" by immediately calling the National Archives, he added.
The classified documents found inside the Penn Biden Center closet are reportedly US intelligence memos and briefing materials that covered topics including Ukraine, Iran and Britain.
US Attorney General Merrick Garland is said to have tasked the US Attorney for the Northern District of Illinois John Lausch Jr. with reviewing the matter.
US Congressman James Comer, a Republican who chairs the House Oversight Committee, told CNN that he plans to press the National Archives, which his committee oversees, for information about the classified documents.
The US Department of Justice is also investigating former President Donald Trump's handling of a trove of classified documents seized from his estate in Mar-a-Lago, Florida, by federal agents in the summer of 2022.
Trump, a Republican, responded to the news of classified documents found at the Penn Biden Center, posting on social media on Monday that "when is the FBI going to raid the many homes of Joe Biden, perhaps even the White House?"
"President Biden has been very critical of President Trump mistakenly taking classified documents to the residence or wherever, and now it seems he may have done the same," Comer said. "How ironic."
The Presidential Records Act requires all presidential and vice-presidential documents to be turned over to the National Archives.