The U.S. Justice Department was searching President Joe Biden's second home, a beach house in Rehoboth, Delaware, on Wednesday as part of its investigation into improper storage of classified materials from his time as vice president.

Biden's personal attorney, Bob Bauer, said in a statement that the search was planned and conducted with the president's "full support and cooperation."

The search by FBI agents appears to represent an expansion of the probe into Biden's handling of classified documents. Materials were earlier found at his home in Wilmington, Delaware, and an office he used during the time between his service as vice president under Barack Obama and his presidential election.

The issue has created a political headache for Biden, who is expected to announce a re-election campaign in the coming weeks or months. It has stripped him and fellow Democrats of a weapon against former President Donald Trump, who also had classified documents found at his home.

Trump has launched his own re-election campaign and could face Biden in the 2024 general election.

Bauer said the Department of Justice chose to do the search without advance notice to the public.

"Under DOJ's standard procedures, in the interests of operational security and integrity, it sought to do this work without advance public notice, and we agreed to cooperate," he said.

"The search today is a further step in a thorough and timely DOJ process we will continue to fully support and facilitate. We will have further information at the conclusion of today’s search."

Classified documents have also been found in the home of Trump's former vice president, Mike Pence, giving some political cover to Biden.

Biden has vowed to cooperate with the searches and Pence had said he takes responsibility for the found documents. Trump resisted efforts to return materials in his possession, prompting a FBI search of his Florida home and resort last year.

U.S. Attorney General Merrick Garland has appointed two separate special counsels to review Trump and Biden's handling of such documents.

Meanwhile, the National Archives has reportedly asked all former U.S. presidents and vice presidents to search their personal records for classified documents or other presidential material that should have been turned over when they left office.

It is unlawful to knowingly or willfully remove or retain classified material, although no current or former president or vice president has been charged with wrongdoing.