Documents stored at former President Donald Trump's Florida home were likely concealed as part of an effort to obstruct an FBI investigation, Department of Justice officials say.

In a court filing, the department said "efforts were likely taken to obstruct" the investigation into Mr Trump's handling of classified material.

The filing was a response to Mr Trump's request for an independent party to oversee part of the ongoing case.

Mr Trump denies wrongdoing.

Upon leaving office, US presidents must transfer all of their documents and emails to the National Archives. The FBI is investigating whether Mr Trump improperly handled records by taking them from the White House to Mar-a-Lago after he left office in January 2021.

In the filing released on Tuesday, the justice department's counterintelligence chief, Jay Bratt, gave the clearest picture so far of the department's attempts to retrieve documents from the former president.

Those attempts led to a National Archives team visiting his Mar-a-Lago home in January and retrieving 15 boxes of White House records that contained "highly classified reports", some of which were "intermixed with other records" and even contained Mr Trump's "handwritten notes".

Also included in the department's filing was a photograph of colour-coded documents apparently taken during the search. It shows various files spread out across a carpet with some marked "Secret" and "Top Secret".

Mr Trump responded to the filing on Wednesday, claiming without evidence that FBI agents "threw documents haphazardly all over the floor (perhaps pretending it was me that did it!)".

"[They] then started taking pictures of them for the public to see," he wrote on his Truth Social platform.

Unlike the released affidavit requesting the original search warrant, whose heavy redactions were cited by Mr Trump and his supporters as evidence of nefarious behaviour, this court filing is a much clearer read.

In its 54 pages, it attempts to knock down allegations by the former president that the Mar-a-Lago search wasn't just unnecessary but part of a political vendetta.

It details government efforts to convince Mr Trump and his lawyers to provide relevant documents voluntarily and the growing concern that they were being less than forthcoming. Suspicions were confirmed, the government said, by the ease with which the FBI found additional classified material.

What the brief doesn't answer is why Mr Trump took the documents to Florida and why he kept them there in the face of a federal investigation that was clearly growing in seriousness.

The old Washington adage that "it's not the crime, it's the cover-up" underscores that some of the biggest political scandals blossom only after the investigatory spotlight is turned on.

There's still no indication of when, or if, Mr Trump or his associates will be criminally charged in this case, but this brief suggests that if they are, it could be a mess of their own making.

After discovering the 15 seized boxes contained "highly classified reports", the justice department and the FBI began investigations which found evidence that "dozens of additional boxes" likely containing classified information still remained at Mar-a-Lago.

On 3 June, three FBI agents and a justice department lawyer arrived at Mar-a-Lago to collect materials. According to Mr Trump's lawyers, he told them: "Whatever you need, just let us know."

But agents were "explicitly prohibited" by his representatives from searching any boxes inside a storage room at Mr Trump's property, according to the latest filing.

Mr Bratt, from the justice department, said this gave "no opportunity for the government to confirm" that no classified documents remained at the property.

Evidence was also found that the records were "likely concealed and removed" from the storage and that efforts were "likely taken" to obstruct the investigation, officials said.

Following the June visit, FBI teams searched Mr Trump's property again in August - where they found more than 100 classified documents. This was twice as many classified documents found "in a matter of hours" than by the "diligent search" that Mr Trump's team claimed they had previously carried out.

Mr Bratt said that this "casts doubt on the extent of co-operation in this matter".

Some agents conducting the review even "required additional clearances before they were permitted to review certain documents", he added.

At the time, Mr Trump rejected reports he had mishandled official records as "fake news".

He is suing for a detailed list of exactly what was taken from his estate, and is asking for the government to return any item which was not in the scope of the search warrant.

Mr Trump's lawyers have asked that a "neutral" third-party attorney - known as a special master - be brought in to determine whether the seized files are covered by executive privilege, which allows presidents to keep certain communications under wraps.

But the latest court filing said that any presidential records seized in the search warrant "belong to the United States, not to the former president".