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Former White House National Security Adviser Michael Flynn is being investigated by Special Counsel Robert Mueller for his involvement in an unfinished documentary film financed by Turkish interests, The Wall Street Journal reported Friday evening. The investigation is part of a larger inquiry to determine if Flynn improperly hid financial ties to both Turkey and Russia, the Journal said.

The FBI is gearing up to interview people Flynn hired to make the documentary, the paper said. That film would have revolved around exiled Turkish cleric, Fethullah Gulen, whom Ankara has accused of trying to overthrow Turkish President Recep Tayyip Edorgan last year, people familiar with the investigation told the Journal.

Gulen, who lives in Pennsylvania, has denied being involved in the attempt to remove Erdogan.

While campaigning for Trump, Flynn’s company reportedly signed a $530,000 deal with a Turkish businessman who was close with Erdogan.

But, according to the Journal, the Flynn Intel Group, Flynn’s consulting firm, tried to mask its role in the documentary. That’s according to David Enders, a journalist employed to film interviews. Enders said that Bijan Kian, Flynn’s business partner, wanted the people behind the film’s production to remain unknown.

A spokesman for Mueller declined the Journal’s request for comment. Kian didn’t reply and Flynn’s lawyer, Robert Kelner, wasn't immediately available to discuss the report, the Journal said.

Flynn didn’t file federal documents showing that he was paid to work for Turkish interests until March 2017. He resigned his position as national security adviser in February following revelations that he misled Vice President Mike Pence about his communications with Russia’s ambassador to the U.S., Sergey Kislyak.

In addition to the probe into whether Flynn improperly concealed his financial ties to Turkey and Russia, Mueller is also reportedly investigating a meeting where Flynn allegedly discussed a plan that would pay him and his son up to $15 million to kidnap Gulen for the Turkish government.

The news follows recent reports that Flynn’s lawyers cut ties with President Donald Trump’s legal team, saying that they could no longer discuss Mueller’s probe into Russian interference during the 2016 election season. The move could indicate that Flynn's legal team either is cooperating with Mueller's investigators or is negotiating to do so.