Biden 'cooperating fully' with review on classified documents

US President Joe Biden says he is cooperating fully with a Justice Department review into some classified documents from his vice presidency that were found in an office he formerly used.

Biden has acknowledged that the documents were discovered in the private office at a Washington think tank last year.

He told reporters in Mexico on Tuesday that he was "briefed about the discovery and surprised to learn that there were any government records that were taken there to that office."

Biden said he did not know what was in the documents.

US broadcaster CNN quoted a source familiar with the matter as saying the documents, dated between 2013 and 2016, contained intelligence memos and briefing materials that covered topics including Ukraine and Iran.

US presidents and vice presidents are legally required to hand over all documents related to their duties to the National Archives when they leave office.

In the past, Biden had criticized his predecessor Donald Trump for taking classified documents out of the White House to his personal residence in Florida.

He now faces growing criticism from Republican lawmakers who want to know why the discovery of documents in his own office were not made public sooner.