Roger Stone. Hollis Johnson

Roger Stone, a longtime informal adviser to President Donald Trump and past Republican politicians, told Yahoo News in an interview published Monday that former Trump campaign chairman Paul Manafort had confirmed to him that investigators said they plan to indict him as part of the FBI's Russia probe.

Manafort is currently a focus in special counsel Robert Mueller's investigation into Russian interference in the 2016 election. That investigation includes scoping out whether members of the Trump campaign colluded with Moscow to help tilt the election in Trump's favor, and Manafort is one of several Trump associates Mueller is looking into.

It emerged in August that the FBI conducted a predawn raid on Manafort's home in July, and agents working with Mueller left Manafort's home "with various records." The New York Times reported last week that following the raid, investigators working with Mueller told Manafort he was going to be charged with a crime.

Stone told Yahoo that he had asked Manafort if the reports were true.

"[Manafort] said, 'Yes,'" Stone said, recalling his conversation with the former campaign chairman. He added that when he asked Manafort if he knew when he'd be indicted, Manafort replied that he did not.

"Do you know for what?" Stone recalled asking Manafort. "He said, 'No.' Pretty straightforward," Stone said.

Manafort has said he's cooperating with investigators, but the search warrant obtained by the FBI prior to July's raid suggests that Mueller managed to convince a federal judge that Manafort would try to conceal or destroy documents subpoenaed by a grand jury.

Manafort is reportedly being scrutinized for possible financial and tax crimes, his contacts with Russian officials, and his work as a foreign agent for entities linked to the Kremlin, particularly Ukraine's pro-Russia Party of Regions.

Paul Manafort AP Photo/Mary Altaffer

Last week, it emerged that US investigators obtained a FISA warrant to wiretap Manafort before and after the election. It was later reported that Manafort offered "private briefings" about the campaign to Oleg Deripaska, a Russian oligarch and ally of Russian President Vladimir Putin, just before the Republican National Convention last year.

The recent revelations and increased focus on Manafort indicate that Mueller is zeroing in on the former Trump campaign chairman as part of a likely attempt to flip him as a witness against Trump.

But Stone told Yahoo that Manafort is still "completely loyal" to the president and is in an "amazingly good mood" despite the Russia firestorm.

Stone added that when he reached out to Manafort following The Times' report alleging that prosecutors planned to indict him, Manafort sounded "very combative" and told him he believes Mueller's team is "guilty of multiple violations of the law and due-process in their efforts to investigate him," according to Yahoo.

When reached, Manafort's spokesman declined to comment.

Manafort reportedly viewed the raid on his home as an "intimidation tactic" to get him to flip against Trump. It's unclear if the raid itself was carried out, in part, to coerce Manafort's cooperation, but legal analysts agree that the speed and aggression with which Mueller is homing in on Manafort is a classic sign that the special counsel wants to flip him as a witness.

"The tactic that Mueller is using — telling Manafort that he will be charged — is generally used when prosecutors are trying to get a defendant to 'flip,'" former federal prosecutor Renato Mariotti wrote last week. The best way to do that, he added, is to assemble enough evidence to make it likely that the individual, if charged, would be convicted and sentenced to jail time.

Manafort, Stone said, still maintains that he hasn't broken any laws. "The notion that [prosecutors] could go to Manafort, for example, and say 'All right, Manafort, we've got you on money laundering, tax evasion, whatever. But if you'll just tell us that you were colluding with the Russians, and Trump knew everything, we'll let you walk.' That's not going to work," Stone said. "That might work with a drug dealer, I don't think it'll work in this case."

It's hard to tell what Mueller has on Manafort, "but they absolutely have something because they got a search warrant," said Joseph Pelcher, a former FBI counterintelligence agent who was stationed in Russia and specialized in organized crime. "You need probable cause to get a search warrant, so there is something there, without question."

Pelcher added that if he were investigating Manafort and found evidence of possible wrongdoing, "the first thing I would do is sit Manafort down and get him to cooperate, because he's not the big fish here."