Two days after a first revelation, new confidential documents were found at Joe Biden's house.
They date from the time of his vice-presidency and were discovered in his private residence in Wilmington, the White House said on Thursday.
The President of the United States assured "fully cooperate" with American justice during a brief exchange with the press.
A dozen documents of this type had already been discovered in a former office of Joe Biden in Washington.
His lawyers then decided to inspect his two private residences, where archives "could have been transferred during the 2017 transition", explained in a press release the lawyer for the presidency, Richard Sauber.
They then found "a small number of additional documents dating from the Obama-Biden administration and classified as confidential", which were in the garage of his home in Wilmington, Delaware, and in an adjoining room, he said. precise.
No documents were found at his residence in the seaside town of Rehoboth in the east coast state, Sauber added, noting that the Justice Department was immediately notified to take possession of the records.
1978 Act
The revelations are embarrassing for the Democratic president, with authorities investigating his Republican predecessor Donald Trump's handling of his own presidential archives for months.
The federal police had carried out a spectacular search in August of the private club in Mar-a-Lago, Florida, where the billionaire has lived since his departure from the White House.
The FBI had seized thousands of documents, including a hundred classified secret-defence.
A 1978 law obliges American presidents and vice-presidents to transmit all their e-mails, letters and other working documents to the National Archives.