The Washington Post is reporting that classified documents related to nuclear weapons were among the items agents sought by federal agents at Mar-a-Lago.

Multiple sources familiar with the investigation told ABC News that the Justice Department and the FBI believed Trump continued to keep sensitive classified documents that had national security implications and that in recent weeks additional information came in suggesting that Trump was not complying with requests to provide the information the Justice Department believed he had in his possession.

Multiple sources familiar with the investigation told ABC News that the Department of Justice and the FBI believed former President Donald Trump continued to keep sensitive classified documents that had national security implications, and that in recent weeks additional information came in suggesting Trump was not complying with requests to provide the information the Justice Department believed he had in his possession.

The information was sensitive enough that authorities wanted to take it back into possession immediately.

-ABC News' Pierre Thomas, Alexander Mallin, Luke Barr, Katherine Faulders, and John Santucci

Former President Donald Trump is calling for "the immediate release" of the warrant that allowed FBI agents to search his Mar-a-Lago estate on Monday.

"Not only will I not oppose the release of documents related to the unAmerican, unwarranted, and unnecessary raid and break-in of my home in Palm Beach, Florida, Mar-a-Lago, I am going a step further by ENCOURAGING the immediate release of those documents, even though they have been drawn up by radical left Democrats and possible future political opponents, who have a strong and powerful vested interest in attacking me much as they have done for the last 6 years," Trump wrote late Thursday in a post on his social media platform, Truth Social.

"This unprecedented political weaponization of law enforcement is inappropriate and highly unethical," he added. "The world is watching as our Country is being brought to a new low, not only on our border, crime, economy, energy, national security, and so much more, but also with respect to our sacred elections!"

-ABC News' Katherine Faulders

The Trump team has said that the documents seized from Mar-a-Lago in this week's FBI raid were declassified. But whether or not they were classified may not matter for two of the criminal statutes cited in the warrant, according to ABC News chief legal analyst Dan Abrams.

"As I look at these statutes, I'm focused less on the question that the Trump team has been talking about, which is the classification of the documents -- which is obviously very important in a macro picture -- but in a strictly legal sense, [for] two of these three statutes, that may not even be the critical question," Abrams told ABC's David Muir in a special report on Friday following the release of the search warrant.

One of the statutes, 18 USC 1519, relates to the destruction, alteration or falsification of records.

"That is the statute I am singularly most interested in here," Abrams said.

The search of the Mar-a-Lago estate was for classified documents, according to the warrant.