(CNN) -- The special master overseeing the Mar-a-Lago documents investigation has ordered former President Donald Trump's lawyers to back up out-of-court assertions that the FBI may have planted evidence at the property during their search last month.

Judge Raymond Dearie, the court-appointed special master, said in a filing Thursday that Trump's team needs to submit a sworn declaration saying if they believe the Justice Department included any items on their "inventory" of materials taken from Mar-a-Lago that were not actually seized during the search.

The declaration must include "a list of any specific items set forth in the Detailed Property Inventory that Plaintiff asserts were not seized from the Premises on August 8, 2022," Dearie wrote in the order.

This has come up as an issue in the case because Trump himself, some of his attorneys, and several of his outside Republican allies have publicly claimed that the FBI planted evidence at Mar-a-Lago during the August 8 search.

However, they have offered no evidence to support these accusations.

On Wednesday night, Trump suggested that the FBI planted evidence during the search. He told Fox News' Sean Hannity, "Did they drop anything into those piles" of materials taken from Mar-a-Lago, "or did they do it later?"

When asked by Hannity if there is video of that, Trump said, "Nah, I don't think so."

The judge set a September 30 deadline for Trump's lawyers to submit this sworn declaration. He also asked the Justice Department to submit declarations attesting to key facts regarding the search.

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