U.S. Special Counsel Robert Mueller is investigating an alleged plot under which former national security adviser Michael Flynn agreed to hand over a wanted Muslim cleric to Turkey in exchange for a payment said to be as much as $15 million, U.S. media reported.

The Wall Street Journal reported on November 10 that Flynn and his son, Michael Flynn Jr., had discussed with Turkish representatives ways to hand over cleric Fethullah Gulen, whom Ankara accuses of instigating an attempted coup against Turkish President Recep Tayyip Erdogan in July.

Flynn allegedly discussed the plot at a meeting in New York in December 2016, when he was a member of then U.S. President-elect Donald Trump's transition team.

The probe into the alleged Gulen plot is part of Mueller's larger investigation into alleged improper contacts between Trump representatives and agents of the Russian government during and after the 2016 U.S. presidential election.

After Trump took office, Flynn served as national security adviser for 24 days before being forced to resign for misleading White House officials about his contacts with Russian Ambassador to the United States Sergei Kislyak.

According to NBC, Mueller's investigators are looking into possible money-laundering charges against the Flynns, as well as charges of lying to federal agents.

In the wake of the attempted coup in Turkey, Ankara pressed President Barack Obama's administration to hand over Gulen, who has asylum in the United States, without a formal extradition process.

On November 8, Flynn published an op-ed piece in The Hill that called Gulen "a shady Islamic mullah" and a "radical Islamist."

According to federal disclosures, Flynn's consulting company received $530,000 for work that "could be construed to have principally benefitted...Turkey."

Based on reporting by The Wall Street Journal, Reuters, and NBC