WASHINGTON — The National Archives confirmed on Friday that it had found classified information among documents that President Donald J. Trump had taken with him to his home in Florida from the White House and that it had consulted with the Justice Department about the matter.

The agency “has identified items marked as classified national security information within the boxes,” according to a letter posted on the National Archives and Record Administration website that was sent to Representative Carolyn B. Maloney, Democrat of New York and the chairwoman of the House Oversight Committee, who has been scrutinizing how Mr. Trump handled presidential records.

“Because NARA identified classified information in the boxes, NARA staff has been in communication with the Department of Justice,” said the letter, written by David S. Ferriero, the national archivist.

In the past two weeks, a series of disclosures has raised new questions about whether Mr. Trump followed federal record-keeping laws or mishandled classified information after he left office. The National Archives said in its letter on Friday that the Trump White House had failed to turn over records that included “certain social media records.”

Mr. Ferriero also wrote that “some White House staff conducted official business using nonofficial electronic messaging accounts that were not copied or forwarded into their official electronic messaging accounts.” The archives said it was in the process of obtaining some of those records.

The disclosure that Mr. Trump had classified information among the documents he took with him from the White House has prompted assertions from Democrats of hypocrisy. Mr. Trump made attacking Hillary Clinton’s mishandling of national security materials a centerpiece of his 2016 presidential campaign.

In January, after lengthy negotiations between his lawyers and the National Archives, 15 boxes of materials that Mr. Trump had taken from the White House were sent back to the National Archives. The boxes included items like official letters, White House documents and gifts that are considered presidential records, are government property and were supposed to be housed at the National Archives.

“In June 2018, NARA learned from a press report in Politico that textual presidential records were being torn up by former President Trump and that White House staff were attempting to tape them back together,” the archives said in the letter to Ms. Maloney on Friday.

The letter added: “The White House Counsel’s Office indicated that they would address the matter. After the end of the Trump administration, NARA learned that additional paper records that had been torn up by former President Trump were included in the records transferred to us. Although White House staff during the Trump administration recovered and taped together some of the torn-up records, a number of other torn-up records that were transferred had not been reconstructed by the White House.”

Other new information cast doubt on Mr. Trump’s handling of government records. The New York Times reported that among the documents that were sent back to the National Archives were some that archivists believed were classified. It was also reported that a book scheduled to be released in October by a Times reporter revealed how staff in the White House residence periodically discovered wads of printed paper clogging a toilet, leading them to believe that Mr. Trump had tried to flush them.

The former president’s use of cellphones to conduct official business also could have led to large gaps in the official White House logs of his calls on Jan. 6, 2021, hindering the House select committee’s investigation into the Capitol riot. If Mr. Trump did not preserve cellphone records and failed to turn them over to the National Archives, that could also be a violation of the law.

Ms. Maloney had warned as early as December 2020 that she believed the Trump administration was not complying with the Presidential Records Act. She wrote a letter to Mr. Ferriero, the national archivist, expressing what she called “grave concerns” that the outgoing administration “may not be adequately preserving records and may be disposing of them.”

Weeks after the Capitol riot, Ms. Maloney requested voluminous materials from the National Archives, including documents and communications before, during and after the Jan. 6 attack pertaining to the counting of electoral votes and planned demonstrations and violence. Then, last week, Ms. Maloney announced that she was starting an investigation after reports in The Washington Post that Mr. Trump had been destroying documents and removed boxes to his property in Florida instead of turning them over to the National Archives and Records Administration.

“I am deeply concerned that these records were not provided to NARA promptly at the end of the Trump administration and that they appear to have been removed from the White House in violation of the Presidential Records Act,” Ms. Maloney said in a letter, adding that Mr. Trump’s practice of ripping up documents “could constitute additional serious violations” of federal law.

Reid J. Epstein contributed reporting.