Classified documents from Joe Biden's vice-presidential days were discovered in November by the U.S. president's personal attorneys at a Washington think tank, a White House lawyer said on Monday.

Nearly 10 documents were found at Biden's office at the Penn Biden Center for Diplomacy and Global Engagement, CBS News reported earlier, adding that U.S. Attorney General Merrick Garland had asked the U.S. attorney in Chicago to review the classified documents which were handed over to the National Archives.

The classified material was identified by personal attorneys for Biden on Nov. 2, days before the midterm elections, Richard Sauber, special counsel to the president, said in a statement on Monday.