US Attorney General Merrick Garland on Thursday said he has appointed a special counsel to investigate classified records from President Joe Biden's time as vice president that were found in his home and office.
"I concluded that ... it was in the public interest to appoint a special counsel," Mr Garland said while naming former US attorney for the District of Maryland Robert Hur to "investigate whether any person or entity violated the law in connection with this matter".
Mr Hur was appointed by former president Donald Trump.
The opening of an investigation into Mr Biden's handling of classified material comes months after a separate investigation was launched into Mr Trump's holding of classified documents after his presidency. Mr Garland assigned a special counsel in that case, too.
Biden lawyer Richard Sauber said in a statement that his team would co-operate with the new special counsel and described any mishandling of documents as a "mistake".
"We are confident that a thorough review will show that these documents were inadvertently misplaced, and the President and his lawyers acted promptly upon discovery of this mistake," Mr Sauber said.
The White House on Thursday confirmed the discovery of a second set of classified documents at Mr Biden's home in Delaware.
Mr Sauber said in a separate statement that lawyers had searched Mr Biden's residences in Wilmington and Rehoboth Beach after discovering an initial set of government documents at the Penn Biden Centre in November.
“As was done in the case of the Penn Biden Centre, the Department of Justice was immediately notified and lawyers arranged for the Department of Justice to take possession of these documents,” he said.
In remarks from the White House, Mr Biden said: “My lawyers reviewed other places where documents from my time as vice president were stored and they finished the review last night and they discovered a small number of documents of classified markings in storage areas and file cabinets in my home.”
Mr Sauber said lawyers had found “a small number of additional Obama-Biden administration records with classified markings”, most of them kept in a storage space in the Wilmington residence garage.
A one-page document was found in an adjacent room, he said in a statement.
He did not disclose what level of classification the materials had.
No classified documents were found at Mr Biden's home in Rehoboth Beach.
The White House is contrasting his compliance with investigators with Mr Trump's efforts in delaying and heavily litigating the probe into hundreds of classified documents he held after his presidency, including accusing the FBI of planting evidence.
John Bolton reacts to Biden classified document discovery
About 100 sensitive government files were found during an FBI search at Mr Trump's Mar-a-Lago home and resort in Florida in August.
Mr Trump is potentially facing charges of violating the Espionage Act for his possession of classified documents, and he and his team are facing accusations of obstruction of justice.
“The biggest distinction between the Biden situation and the Trump situation is that from what we can tell, Biden has co-operated with the Justice Department, the National Archives to get it right,” former national security adviser to Mr Trump, John Bolton, told The National on Thursday.
“Unlike Trump, who resisted it tooth and toenail.”
FBI raid on Trump's Mar-a-Lago estate — in pictures
It is not known if Mr Biden viewed the documents after his vice presidency or if there were any intentions behind the possession of the documents.
“Both were in possession of classified material that they shouldn’t have had,” Mr Bolton said.
“There are important legal distinctions, [and] I’m afraid the political fog that we’re going to see is going to come down to Biden had classified documents, Trump had classified documents, it’s the same thing.”
Republicans on Capitol Hill are already calling for action.
“Congress has to investigate,” House Speaker Kevin McCarthy said to reporters on Thursday.
Thomas Watkins and Kyle Fitzgerald in Washington contributed to this story
