The U.S. National Archives discovered more than 700 pages of classified documents at former President Donald Trump's Florida home in addition to material seized this month by FBI agents, according to a newly disclosed May letter the records agency sent to his attorney.

The large quantity of classified material in 15 boxes recovered in January by the National Archives and Records Administration, some marked as "top secret," provides more insight into what led to the FBI's court-authorized Aug. 8 search of Trump's residence at the Mar-a-Lago resort in Palm Beach.

The agency is responsible for preserving government records.