GARLAND: "I strongly believe the normal processes of this department can handle all investigations with integrity. But under the regulations, the extraordinary circumstances here require the appointment of a special counsel for this matter."

Garland said former U.S. attorney Robert Hur would carry out the independent investigation hours after the White House confirmed that Biden's legal team had found a second set of classified papers from his time as vice president in the garage of his Delaware home, in addition to the classified documents discovered in November at a Washington think tank.

The president told reporters on Thursday that he was 'cooperating fully and completely with the Justice Department's review.

BIDEN: "I take classified documents and classified material seriously."

The inquiry could cast a shadow over the Democratic president's expected run for re-election in 2024, and it comes as another special counsel probe is already underway, looking at former president Trump - his handling of classified documents and efforts to overturn the 2020 election.

"I think Congress has to investigate this."

Republican House speaker Kevin McCarthy on Thursday accused the White House of hypocrisy.

"Another faux pas by the Biden administration, but treating law differently based upon your political beliefs."

In Trump's case, FBI agents carried out a search last August at his Mar-a-Lago estate in Florida. About 100 documents marked as classified were among thousands of records seized.

The search came after Trump resisted numerous requests and a subpoena to return the sensitive materials, leading to questions of whether Trump or his staff obstructed the investigation.

Biden says he wasn't aware of the documents. His attorneys say the papers were inadvertently misplaced and were handed over as soon as they were discovered.

But now special prosecutors -- who are typically appointed to politically sensitive cases to ensure independence -- will be looking into both Trump and Biden, just as the two are expected to face off again in 2024 election.