The US justice department is reviewing potentially classified documents found in President Joe Biden's former office at a think tank, the White House says.
About 10 of the files were discovered in a locked closet at the Penn Biden Center in Washington in November by Mr Biden's legal team, said his lawyer.
The batch has been handed over to the National Archives.
Mr Biden's predecessor, Donald Trump, is facing a probe for taking classified files to Florida after his presidency.
According to the BBC's US partner CBS News, the FBI is involved in the inquiry into classified documents found at the Penn Biden Center, and US Attorney General Merrick Garland has been asked to review the papers.
A source familiar with the matter told CBS News the batch did not contain nuclear secrets and had been contained in a folder in a box with other unclassified papers.
Richard Sauber, special counsel to President Biden, said in a statement to CBS on Monday that the files were discovered just before the midterm elections by Biden attorneys who were clearing out the office space.
Mr Biden kept an office at the think tank, which is about a mile from the White House, from 2017 to 2020.
Mr Sauber said: "Since that discovery [of the documents], the president's personal attorneys have co-operated with the [National] Archives and the Department of Justice in a process to ensure that any Obama-Biden Administration records are appropriately in the possession of the Archives."
Mr Trump reacted on Monday on his social media site, Truth Social, asking: "When is the FBI going to raid the many homes of Joe Biden, perhaps even the White House?"
Mr Trump is under investigation for allegedly resisting requests to give back about 300 classified documents that he took to his Florida estate, Mar-a-Lago, after leaving office. The National Archives tipped off the authorities in that case.
The Biden files were discovered shortly before the justice department announced it would appoint an independent lawyer to decide whether to criminally charge Mr Trump over the files found at his golf club.
Congressman James Comer, the new Republican chairman of the House Oversight Committee, said on Monday that the handling of the Biden papers raised questions about the justice department's neutrality.
He told reporters: "This is further concern that there's a two-tier justice system within the DoJ [justice department] with how they treat Republicans versus Democrats, certainly how they treat the former president versus the current president."
Neither the Penn Biden Center nor National Archives immediately commented.
In September, President Biden appeared on CBS and was asked for his reaction to a photo showing the documents recovered at Mar-a-Lago.
"How anyone could be that irresponsible?" the president said.
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