US President Joe Biden has been interviewed over two days by a Special Counsel as part of a probe into his handling of classified documents, the White House has said.

The interview was conducted at the White House on Sunday and Monday, Ian Sams, the spokesperson of the White House Counsel's Office said on Monday.

"The President has been interviewed as part of the investigation being led by Special Counsel Robert Hur. The voluntary interview was conducted at the White House over two days, Sunday and Monday, and concluded Monday," Sams said.

The White House said in January that documents with classified markings were found at Biden’s Delaware home and at a Washington office he used after he was vice president.

"As we have said from the beginning, the President and the White House are cooperating with this investigation, and as it has been appropriate, we have provided relevant updates publicly, being as transparent as we can consistent with protecting and preserving the integrity of the investigation," Sams said.

He refrained from providing any other further details of the probe against 80-year-old Biden.

The interview, scheduled weeks ago, marks the first significant development in the case known to the public in months, a report by CNN said.

Attorney General Merrick announced the investigation and laid out a timeline of the case, which began after the president's attorneys found documents at Biden's former Washington DC office and his Delaware residence in November 2022, the report said.

The interview raises the possibility that the special counsel’s investigation may be nearing its end, NBC News reported.

The documents were found "among personal and political papers," according to a statement from Biden's legal team.

The National Archives informed a Department of Justice prosecutor on November 4 that the White House had made the Archives aware of documents with classified markings found at Biden's think tank, which was not authorised to store classified materials, Garland said.

On November 14, then-US Attorney John Lausch was tasked with leading that preliminary inquiry after the FBI opened an initial assessment, and Lausch was informed on December 20 of the second batch of apparently classified documents being found at Biden's Wilmington home, according to Garland's account.

Hur was subsequently appointed in January to investigate the case, the report said.

According to Politico, the FBI also conducted searches of the Biden vacation home in Delaware, where "some materials and handwritten notes" that appeared to date back to Biden's time as vice president were found, the president's lawyer Bob Bauer said.

Biden said in January that he was surprised to learn that classified documents were found in his former office.

Responding to a question at a news conference in Mexico City, where he was attending a summit, the president said, "I was surprised to learn there were any government records that were taken there to that office," the report said. He emphasised then that he did not know what was in the documents.

The report said that US intelligence memos and briefing materials covered topics including Ukraine, Iran, and the United Kingdom were among them, quoting an informed source.

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