President Joe Biden said on Tuesday he was surprised to learn that classified documents were found in a think-tank office he once used and said he and his team are cooperating fully with a review into what happened.

Biden told reporters at a joint news conference with the leaders of Mexico and Canada that he takes classified documents seriously. He said he did not know what was in the documents.

“We are cooperating fully with the review, which I hope will be finished soon,” said Biden.