A lawyer for former United States President Donald Trump signed a statement in June that said all classified material held in boxes at Mr Trump's Mar-a-Lago residence had been returned to the government, the New York Times reported on Saturday.
The statement was signed after Jay Bratt, a top national security official in the US Department of Justice, visited Mr Trump's South Florida beach club on 3 June.
Mr Bratt met with two of Mr Trump's lawyers to discuss the handling of classified information during the visit, the newspaper said.
What happened at the Mar-a-Lago residence?
Mr Trump is under federal investigation for possible violations of the Espionage Act, which makes it unlawful to spy for another country or mishandle US defence information, including sharing it with people not authorised to receive it, a search warrant made public on Friday showed.
FBI agents searched Mar-a-Lago this week and removed 11 sets of classified documents, including some marked as top secret, according to the Justice Department.
The existence of the statement by an attorney for Mr Trump suggests that Mr Trump and his team may not have fully disclosed information about classified documents in the former president's residence, the Times reported.
Reuters was not able to independently confirm the report. The Justice Department declined to comment.
Taylor Budowich, a spokesperson for Mr Trump, criticised the FBI search in a statement as an "unprecedented and unnecessary raid" that was part of another "Democrat-fabricated witch hunt."
Mr Budowich did not confirm or deny the New York Times report.
Why are there national security concerns?
As president, Mr Trump sometimes shared information, regardless of its sensitivity.
Early in his presidency, he spontaneously gave highly classified information to Russia’s foreign minister about a planned Islamic State operation while he was in the Oval Office, US officials said at the time.
But it was at Mar-a-Lago, where well-heeled members and guests attended weddings and fundraising dinners and frolicked on a breezy ocean patio, that US intelligence seemed especially at risk.
The chairs of the House of Representatives Intelligence Committee and the Committee on Oversight and Reform on Saturday asked the director of national intelligence, Avril Haines, to review what damage may have been done to national security by Mr Trump having the highly classified documents at Mar-a-Lago.
"Former President Trump's conduct has potentially put our national security at grave risk," the two committee chairs, both Democrats, said in a three-page letter, which they publicly released.
Calls for a full review
"This issue demands a full review, in addition to the ongoing law enforcement inquiry."
The Justice Department’s search raises concerns about the threat to national security, former Department of Justice official Mary McCord said.
Supporters of former President Donald Trump rallied near his home at Mar-A-Lago following the FBI executing a search warrant at the residence. Source: Getty / Eva Marie Uzcategui
"Even just retention of highly classified documents in improper storage - particularly given Mar-a-Lago, the foreign visitors there and others who might have connections with foreign governments and foreign agents - creates a significant national security threat."
Mr Trump, in a statement on his social media platform, said the records were "all declassified" and placed in "secure storage."
Ms McCord said, however, she saw no "plausible argument that he had made a conscious decision about each one of these to declassify them before he left."
After leaving office, she said, he did not have the power to declassify information.
