President Trump demanded "total transparency" Wednesday ahead of a meeting between top law enforcement officials and congressional Republicans demanding Russia probe documents.

"They'll all be in the room tomorrow. We'll see what happens. I want total transparency," Trump said on the South Lawn of the White House. "You have to have transparency."

Trump, using the term "spygate" to describe the FBI's reported use of an informant on his campaign, directly referenced Deputy Attorney General Rod Rosenstein, who is supervising special counsel Robert Mueller's probe of possible Trump campaign collusion with Russia.

"What I want from Rod, from the FBI, from everybody, we want transparency. And you know what? I think in their own way, they are obstructionists, but even the Democrats, I really believe on this issue, it supersedes. I think they want transparency, too," he said.

The Justice Department has resisted providing documents to congressional Republicans, warning that outing informants could put lives at risk.

The document-release meeting was scheduled after Trump raged last week about reports of an FBI informant linked to his campaign, suggesting repeatedly that he believed there may have been a "politically motivated" spy on the campaign.

The informant reportedly was Cambridge University professor Stefan Halper, who was not embedded as a spy within the campaign but sought out meetings with Trump campaign advisers Carter Page, George Papadopoulos, and Sam Clovis.

House Intelligence Committee chairman Rep. Devin Nunes, R-Calif., however, has suggested there may be additional informants. The top Democrat on the committee, Rep. Adam Schiff of California, meanwhile, alleged Trump invented the notion of a spy.

On Monday, Trump summoned officials to the White House and tasked chief of staff John Kelly with organizing a meeting between FBI, Justice Department, and spy agency representatives to discuss providing documents to Congress.

Attendees of the Thursday document meeting will include Nunes, House Oversight Committee chairman Rep. Trey Gowdy, R-S.C., FBI Director Christopher Wray, Director of National Intelligence Dan Coats, and Justice Department official Edward O'Callaghan.

The meeting won't have a White House representative, White House press secretary Sarah Sanders said Tuesday.

Trump told reporters Tuesday that he hoped that there wasn't a spy on his 2016 campaign and he continued to equivocate Wednesday.

"I hope it's not true but it looks like it is," he said on the South Lawn.

Trump stood by his criticism of investigative tactics used to determine if his campaign colluded with Russia, and attacked former FBI Director James Comey, who he fired last year.

"We now call it spygate. You're calling it spygate. A lot of bad things have happened. I want them to get together, they'll sit in a room and hopefully work it out among themselves," he said.

"We're not undercutting. We're cleaning everything up. This was a terrible situation. What we're doing is we're cleaning everything up," Trump said. "It's so important. What I'm doing is a service to this country, and I did a great service to this country by firing James Comey."

In addition to the meeting on document requests, Rosenstein on Sunday asked that the Justice Department inspector general review Trump's assertion that there may have been politically motivated spying on his campaign. The review expands an ongoing inspector general probe of the FBI's use of an opposition research dossier compiled by former British spy Christopher Steele to obtain a 2016 surveillance order against Page.