(CNN) -- A lawyer for former Vice President Mike Pence discovered about a dozen documents marked as classified at Pence's Indiana home last week, and he has turned those classified records over to the FBI, multiple sources familiar with the matter told CNN.
The FBI and the Justice Department's National Security Division have launched a review of the documents and how they ended up in Pence's house in Indiana.
The classified documents were discovered at Pence's new home in Carmel, Indiana, by a lawyer for Pence in the wake of the revelations about classified material discovered in President Joe Biden's private office and residence, the sources said. The discovery comes after Pence has repeatedly said he did not have any classified documents in his possession.
It is not yet clear what the documents are related to or their level of sensitivity or classification. Pence's team plans to notify Congress on Tuesday.
Pence asked his lawyer to conduct the search of his home out of an abundance of caution, and the attorney began going through four boxes stored at Pence's house last week, finding a small number of documents with classified markings, the sources said.
Pence's lawyer immediately alerted the National Archives, the sources said. In turn, the Archives informed the Justice Department.
A lawyer for Pence told CNN that the FBI requested to pick up the documents with classified markings that evening, and Pence agreed. Agents from the FBI's field office in Indianapolis picked up the documents from Pence's home, the lawyer said.
On Monday, Pence's legal team drove the boxes back to Washington, DC, and handed them over to the Archives to review the rest of the material for compliance with the Presidential Records Act.
In a letter to the National Archives obtained by CNN, Pence's representative to the Archives Greg Jacob wrote that a "small number of documents bearing classified markings" were inadvertently boxed and transported to the vice president's home.
"Vice President Pence was unaware of the existence of sensitive or classified documents at his personal residence," Jacob wrote. "Vice President Pence understands the high importance of protecting sensitive and classified information and stands ready and willing to cooperate fully with the National Archives and any appropriate inquiry."
The classified material was stored in boxes that first went to Pence's temporary home in Virginia before they were moved to Indiana, according to the sources. The boxes were not in a secure area, but once the classified documents were discovered, the sources said they were placed inside a safe located in the house.
Pence's Washington, DC, office was also searched, Pence's lawyer said, and no classified material or other records covered by the Presidential Records Act was discovered.
The news about Pence come as special counsels investigate the handling of classified documents by both Biden and former President Donald Trump. The revelations also come amid speculation that Pence is readying for a run at the Republican nomination for president in 2024.
Since the FBI searched Trump's home in Florida for classified material in August with a search warrant, Pence has said that he had not retained any classified material upon leaving office. "No, not to my knowledge," he told The Associated Press in August.
In November, Pence was asked by ABC News at his Indiana home whether he had taken any classified documents from the White House.
"I did not," Pence responded.
"Well, there'd be no reason to have classified documents, particularly if they were in an unprotected area," Pence continued. "But I will tell you that I believe there had to be many better ways to resolve that issue than executing a search warrant at the personal residence of a former president of the United States."
While Pence's vice presidential office in general did a rigorous job while he was leaving office of sorting through and turning over any classified material and unclassified material covered by the Presidential Records Act, these classified documents appear to have inadvertently slipped through the process because most of the materials were packed up separately from the vice president's residence, along with Pence's personal papers, the sources told CNN.
The vice president's residence at the US Naval Observatory in Washington has a secure facility for handling classified material along with other security, and it would be common for classified documents to be there for the vice president to review.
Some of the boxes were packed up from the vice president's residence, while some came from the White House in the final days of the Trump administration, which included last-minute things that did not go through the process the rest of Pence's documents did.
The discovery of classified documents in Pence's residence marks the third time in recent history in which a president or vice president has inappropriately possessed classified material after leaving office. Both Biden and Trump are now being investigated by separate special counsels for their handling of classified materials.
Sources familiar with the process say Pence's discovery of classified documents after the Trump and Biden controversies would suggest a more systemic problem related to classified material and the Presidential Records Act, which requires official records from the White House to be turned over to the National Archives at the end of an administration.
On Friday, the FBI searched Biden's Wilmington residence for additional classified material, an unprecedented search of a sitting president's home that turned up six additional items containing classified markings. The search was conducted after Biden's lawyers discovered classified material in Wilmington following the initial discovery of classified documents at Biden's private think office in November.
Biden's attorneys say they are fully cooperating with the Justice Department, seeking to draw a distinction from the Trump investigation.
The FBI obtained a search warrant to search Trump's Mar-a-Lago resort in August. Federal investigators took that step because they believed Trump had not turned over all classified material despite a subpoena and were concerned records at Mar-a-Lago were being moved around.
Last week, Pence told Larry Kudlow in a Fox Business interview that he received the President's Daily Brief at the vice president's residence.
"I'd rise early. I'd go to the safe where my military aide would place those classified materials. I'd pull them out, review them," Pence said. "I'd receive a presentation to them and then, frankly, more often than not Larry, I would simply return them back to the file that I'd received them in. They went in commonly into what was called a burn bag that my military aide would gather and then destroy those classified materials—same goes in materials that I would receive at the White House."
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