US President Joe Biden has been interviewed on a voluntary basis about his handling of classified documents when he was vice president.

In a statement on Monday, the White House said Special Counsel Robert Hur conducted the interviews over two days at the White House. It said the interviews concluded Monday and that the president and the White House are cooperating with the investigation.

The US Justice Department appointed a special counsel to lead an investigation after classified documents were discovered at Biden's private office and his residence.

US media report that the interviews suggest that the investigation is coming to an end.

Former US President Donald Trump was indicted in June on criminal charges including storing classified documents about nuclear weapons and military capabilities.