WASHINGTON -- Republicans stepped up calls on Sunday for the release of an FBI affidavit showing the underlying justification for its seizure of documents at former President Donald Trump's Mar-a-Lago home.

A search warrant released last week after the unprecedented search showed that Trump had 11 sets of classified documents at his home, and that the Justice Department had probable cause to conduct the search based on possible Espionage Act violations.

Republicans are calling for the disclosure of more detailed information that persuaded a federal judge to issue the search warrant, which may show sources of information and details about the nature of the documents and other classified information. The unsealing of such affidavits is highly unusual and would require approval from a federal judge.

"I think a releasing the affidavit would help, at least that would confirm that there was justification for this raid," Republican Senator Mike Rounds told NBC's "Meet the Press."

"The Justice Department should "show that this was not just a fishing expedition, that they had due cause to go in and to do this, that they did exhaust all other means," Rounds said. "And if they can't do that, then we've got a serious problem on our hands."

The Department of Justice did not immediately respond to a request for comment.

Representative Mike Turner, the top Republican on the House Intelligence Committee, said on CNN on Sunday that the Biden administration should provide more details on what led to the raid.

"Congress is saying, 'Show us. We want to know what did the FBI tell them? What did they find?'" Turner said.

Representative Adam Schiff, the California Democrat who chairs the House Intelligence Committee, did not address the issue of the affidavit on Sunday.

He said it was "most disturbing" that Trump continued to hold the classified documents after the Justice Department sought their return. "It appears to be wilful on the president's part, the keeping of these documents after the government was requesting them back," he told CBS' "Face the Nation."

(Reporting by David Lawder; Editing by Heather Timmons and Lisa Shumaker)