BREAKING: SECOND BATCH of classified documents discovered by Biden aides

A source close to the matter said that aides have been searching for any additional classified documents since the first batch of documents were discovered in November, prior to the midterm elections, NBC News reports. The source spoke on condition of anonymity.

CBS News first reported that classified documents were found in an office Biden used during his vice presidency.

It was reported on Tuesday by another anonymous source that the intelligence materials discovered were related to Ukraine, Iran, and the UK.

A source familiar with the matter told CNN that the documents are US intelligence briefings and memos related to topics including Ukraine, Iran, and the United Kingdom, and were dated between 2013 and 2016.

On Monday, it was announced that US Attorney General Merrick Garland assigned an attorney to review classified documents found at the Penn Biden Center for Diplomacy and Global Engagement in Washington. This relates to about 10 documents from President Biden's vice-presidential office, two sources said.

The materials were identified by personal attorneys for the president on November 2, just days before the midterm elections, according to special counsel to the president Richard Sauber. The documents were discovered when Biden's personal attorneys "were packing files housed in a locked closet to prepare to vacate office space at the Penn Biden Center in Washington, DC," Sauber said in a statement.

This is a breaking story and will be updated.