The FBI was pursuing a secret investigation into Russian election interference and President Donald Trump's campaign 100 days before Election Day, according to a New York Times report.

The investigation was nicknamed "Crossfire Hurricane."

Information gathered reportedly contributed compelling evidence in favor of the controversial surveillance of Carter Page.

The New York Times reported FBI agents started a secret investigation into Russian election interference and President Donald Trump's 2016 campaign called "Crossfire Hurricane" just 100 days before Election Day.

The investigation added to the political firestorm started earlier that year by the agency's investigation into Hillary Clinton's use of a private email server, which has been credited with pushing Trump toward electoral victory.

Agents reportedly avoided interviewing Trump associates and subpoenaing documents to keep the investigation secret. Only about five Justice Department officials were aware of the case, according to officials cited in the story, in contrast to the dozen who would normally be briefed on such a national security matter.

"Crossfire Hurricane," a reference to a Rolling Stones lyrics, continued in secret as Trump publicly railed against the investigation, calling it a "witch hunt."

The Trump campaign aides interviewed because of potential Russian ties included former national security adviser Michael Flynn, former campaign chairman Paul Manafort, and former foreign policy advisers Carter Page and George Papadopoulos, current and former officials told the Times.

Page ended up at the center of controversy when Republicans said the FBI had overstepped its authority in surveillance of Page, who had reportedly been known to the FBI since 2013 for previous contact with Russian spies.

The previously secret assignment began with an August 2016 FBI interview of the Australian ambassador about his meeting with Papadopoulos to evaluate evidence a campaign adviser knew about Russian meddling.