Classified documents from the time when Joe Biden was serving as Barack Obama's vice president have been found at a Washington think tank that Biden sometimes used as office space, the White House said Monday. Lawyers for Biden discovered the documents last November while clearing out the office space and handed them over to the National Archives, which handles all such materials, Biden's special counsel Richard Sauber said. "The White House is cooperating with the National Archives and the Department of Justice," Sauber said in a statement. Sauber described it as "a small number of documents with classified markings" that were found at the Penn Biden Center, a think tank affiliated with the University of Pennsylvania. He said they were in a locked closet at the time, AFP reported. "The documents were not the subject of any previous request or inquiry" and since handing them over, Biden's attorneys have also cooperated "to ensure that any Obama-Biden Administration records are appropriately in the possession of the Archives," he said. CBS News reported that Attorney General Merrick Garland has assigned the US attorney in Chicago to review the documents and that the FBI is also investigating. According to the report, about 10 documents are involved and an unidentified source familiar with them said none contain nuclear secrets. In August, authorities searched ex-president Donald Trump's residence at Mar-a-Lago after he failed to respond to repeated requests for cooperation on retrieving documents taken from the White House after his 2020 election loss. The FBI found thousands of government documents, including more than 100 that were marked classified, and some marked top secret in the ex-president's Florida club. Subjects covered in the documents reportedly included sensitive intelligence on China and Iran, and nuclear secrets. "When is the FBI going to raid the many homes of Joe Biden, perhaps even the White House? These documents were definitely not declassified," Trump said in a brief statement after the discovery of the documents at the think tank emerged Monday.