A US judge on Thursday refused to let the Department of Justice resume reviewing classified records seized by the FBI from former president Donald Trump's Florida estate in a continuing criminal investigation.
Federal Judge Aileen Cannon also appointed Senior District Judge Raymond Dearie of New York as special master to review the seized records for material that could be privileged and kept from federal investigators.
Mr Dearie will be responsible for reviewing the documents taken during the August raid of Mar-a-Lago and separating any that may be covered by claims of privilege. A November deadline was set for this process.
In the meantime, Ms Cannon continued to block the Justice Department from using about 100 classified documents in its investigation of Mr Trump's handling of classified records since leaving office.
The order will almost certainly slow the department's investigation and be challenged in a federal appeals court.
The Justice Department did not immediately comment on the judge's order.
Ms Cannon said she was not prepared to accept the government's characterisations of the documents, saying “even-handed procedure does not demand unquestioning trust in the determinations of the Department of Justice”.
The FBI says it recovered more than 11,000 documents from the home during its search, including more than 100 with classification markings.
The Trump team recommended either Mr Dearie or a Florida lawyer for the job.
The Justice Department said that, in addition to the two retired judges whose names it submitted, it would also be satisfied with Mr Dearie's appointment.
Lawyers for the department had argued against the appointment of a special master, saying the investigation would be harmed if the judge did not lift her block on it, citing national security concerns.
Ms Cannon rejected that idea on Thursday, saying “there has been no actual suggestion by the government of any identifiable emergency or imminent disclosure of classified information arising from [Mr Trump's] allegedly unlawful retention of the seized property”.
“Instead, and unfortunately, the unwarranted disclosures that float in the background have been leaks to the media after the underlying seizure,” she added.
Mr Dearie was the top federal prosecutor for the Eastern District of New York from 1982 to 1986, at which point he was appointed to the federal bench by then-president Ronald Reagan.
He has also served on the Foreign Intelligence Surveillance Court, which authorises Justice Department wiretap applications in investigations involving suspected agents of foreign powers.
Agencies contributed to this report