A “small number of documents” with classified markings that appear to be from the Obama administration were found at a think tank in Washington, D.C., tied to President Joe Biden and are under review by the Justice Department and National Archives, a White House lawyer said Monday.

The documents were discovered in a locked closet by Biden’s attorneys days before the midterm elections as they prepared to vacate office space at the Penn Biden Center for Diplomacy and Global Engagement, Richard Sauber, special counsel to the president said in a statement.

A source familiar with the matter told NBC News that Biden only became aware of the classified documents being stored in his former office when he was informed by his lawyers they had discovered them.

CBS News first reported on the documents.

Sauber said that the White House is cooperating with the Justice Department and National Archives regarding the discovery of the documents found in an office that Biden “periodically” used from mid-2017 until the start of his 2020 presidential campaign.

“The White House is cooperating with the National Archives and the Department of Justice regarding the discovery of what appear to be Obama-Biden Administration records, including a small number of documents with classified markings,” Sauber said.

A source familiar with the matter confirmed that Attorney General Merrick Garland asked the U.S. Attorney for the Northern District of Illinois, John R. Lausch, to review the matter of how classified material ended up at the Penn Biden Center. The review was intentionally assigned to Lausch, a holdover Trump appointee, to avoid any conflict of interest, the source said.

According to Sauber, the classified material was discovered on Nov. 2 by Biden’s personal attorneys, and the White House Counsel’s Office notified the National Archives, which took possession of the materials the following morning.

“The documents were not the subject of any previous request or inquiry by the Archives,” Sauber said. “Since that discovery, the President’s personal attorneys have cooperated with the 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.”

News of the found documents comes about five months after FBI agents executed a search warrant at former President Donald Trump’s Mar-a-Lago resort in Florida. The search uncovered more than 100 documents with classification markings, including some that were marked top secret.

Last month, two more documents with classified markings were found in a Florida storage facility not far from Trump’s Palm Beach resort and were turned over to the FBI.

Trump posted on his Truth Social account about the documents from the Penn Biden Center, saying, “When is the FBI going to raid the many homes of Joe Biden, perhaps even the White House? These documents were definitely not declassified.”

Rep. James Comer, the new chair of the House Oversight and Accountability Committee, told reporters Monday night that he plans to send a letter to the White House Counsel’s Office and the National Archives requesting information about the Biden-related documents.

The Kentucky Republican added that based on research by his investigators following the Mar-a-Lago search, it was not uncommon for former presidents to accidentally leave office with classified documents.

Comer made clear that he thought it was unlikely Biden did anything wrong by taking the documents, and that he was more concerned that Trump may have been treated unfairly.

“There are a lot of people in America that think there’s a two tier justice system in America. That there’s a difference in the way Republicans and Democrats are treated,” Comer said.

After leaving office in January 2017, Biden was named the University of Pennsylvania’s Benjamin Franklin Presidential Practice Professor and the head of its new think tank. The school formally opened a suite of offices for the center in February 2018, including an office for Biden’s personal use when he was in Washington.

During a 2018 interview after the formal opening of the offices, Biden told MSNBC: “I don’t have access to classified information anymore.”

Biden did not answer shouted questions from reporters on Monday, ahead of a bilateral meeting with President Andrés Manuel López Obrador of Mexico, about how classified documents were found in his private office.