Donald Trump has asked a US federal court to block the FBI from reviewing materials seized from his Mar-a-Lago home, pending the appointment of a special master.

The former US president filed the motion in Florida, which also demanded more details about what was taken by the FBI during the raid.

Classified documents were reportedly found during the search, some labelled "top secret" — the highest level of classification for security information that is only supposed to be viewed in specific government facilities.

But Trump's motion to the court says he wants a neutral third party to look through the documentation before the investigation resumes.

Here's what we know about the latest development in the long-running saga.

What is a 'special master'?

A special master can be appointed in some highly sensitive cases to go through seized materials and ensure that investigators don't review privileged information.

Cornell Law School's Legal Information Institute describes a special master as someone "appointed by a court to carry out some sort of action on its behalf".

Trump's request has been assigned to US District Judge Aileen M Cannon, who was nominated by Trump himself when he was still in office.

The former US president requested a special master without existing connections to the case, calling to appoint someone with a "fair-minded approach". 

The US Attorney's office in Manhattan requested the appointment of a special master when the FBI searched the homes of Michael Cohen and Rudy Giuliani, Trump's former lawyers, prior to the Mar-a-Lago raid. 

In those instances, the position was filled by a retired judge.

What do the documents say?

The 27-page motion refers to the former president as "President Donald J Trump" repeatedly, as well as declaring that he is the "clear frontrunner in the 2024 Republican Presidential Primary and in the 2024 General Election, should he decide to run".

It seeks: 

• The appointment of a special master
• A halt on the review of seized materials until a special master is appointed
• A "more detailed Receipt for Property" from the government
• The return of any items that are "not within the scope" of the search warrant

The court filing calls the FBI's raid a "shockingly aggressive move" that caused distress to "most Americans", and alleges that some of the items taken were "outside the lawful reach of an already over-broad warrant". 

The search conducted earlier this month was part of a federal investigation into whether Trump illegally removed documents when he left office in January 2021.

The lawsuit argues that the records, created during Trump's time as US president, are "presumptively privileged" and that "only an evaluation by a neutral reviewer ... can secure the sanctity of these privileged materials".

But the Supreme Court has never determined whether a former president can assert executive privilege over documents.

Why now?

Well, that's what a lot of commentators are asking.

Trump released a statement saying his Mar-a-Lago home was "under siege" two weeks ago.

This latest request asks for the review of the documents seized from his home to stop until a special master is appointed — but it's likely a significant chunk of that review has already occurred.

Journalist Eric Tucker, who covers the FBI and Justice Department for The Associated Press, reports that it's unclear whether Trump has now waited too long to seek the appointment of a special master.

A spokesperson for the Justice Department said prosecutors would file their response to the motion in court.

ABC/wires