A secret FBI informant who has come into the spotlight in recent days reportedly met with three advisers to President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE's campaign during the 2016 presidential election.

The Washington Post reported Friday that in addition to meeting with Trump campaign advisers George PapadopoulosGeorge Demetrios PapadopoulosTale of two FBI cases: Clinton got warned, Trump got investigated Trump says he would consider pardons for those implicated in Mueller investigation New FBI document confirms the Trump campaign was investigated without justification MORE and Carter Page, the informant — described as an American academic — also met with former Trump campaign co-chairman Sam Clovis.

The informant, a retired professor who is said to be a longtime U.S. intelligence source, met Clovis for coffee in Northern Virginia in the summer of 2016, during which he offered to provide foreign policy advice to the campaign, the Post reported.

The New York Times had previously reported on Wednesday that the informant approached Papadopoulos and Page.

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The role of the informant in the origins of the FBI investigation into possible ties between the Trump campaign and Russia has given rise to claims by some GOP lawmakers and Trump allies in recent days that the Obama administration planted a "mole" within the Trump campaign to dig up dirt on the businessman and his associates.

There is no evidence that the FBI dispatched the informant to infiltrate the Trump campaign, the Times reported Friday.

The use of informants is relatively common, and they are typically used before other methods of intelligence gathering, like electronic surveillance.

But exactly how the informant became involved in the Russia investigation and how much information he provided to the FBI remains unclear.

The focus on the informant's role by some conservatives and allies of Trump has reportedly sparked concern at the FBI, where officials have sought in recent weeks to mitigate the potential damage if the source's identity is exposed.

The Times reported Friday that the source, whom it described as an academic who has worked in Britain, is well known in Washington circles and has acted as an informant for the CIA for years.

Still, the informant has raised alarm bells for some Republicans, including House Intelligence Committee Chairman Devin Nunes Devin Gerald NunesSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Sunday shows preview: With less than two months to go, race for the White House heats up Sunday shows preview: Republicans gear up for national convention, USPS debate continues in Washington MORE (R-Calif.), who earlier this month subpoenaed the Justice Department for documents related to the source.

The Justice Department declined to provide the records out of concern that it could endanger the informant and his associates.

Trump himself has also seized on reports that the informant met with campaign advisers, suggesting on Thursday that the Obama administration had improperly spied on his campaign, and that, if so, it could end up being "bigger than Watergate."