The US Justice Department has appointed a special counsel to lead an investigation into the discovery of classified documents at President Joe Biden's private office and elsewhere.

The department announced the appointment on Thursday.

Classified documents were discovered in November at Biden's private office in Washington. Another batch was found in a separate location.

The records are from the time he was vice president.

Biden has said he was surprised by the discovery, and his team is cooperating with a review into why they were there.

A special counsel is a prosecutor who investigates cases where there might be a conflict of interest for authorities. The system was also used to probe classified documents found at the home of former President Donald Trump.