Flynn resigned as Trump's national security adviser on February 13 after only 24 days on the job.
The alleged plan would have involved Flynn and his son, Michael Flynn Jr., delivering Fethullah Gulen to the Turkish government, which views Gulen, whom the U.S. government has refused to extradite, as a political enemy.
Special counsel Robert Mueller is investigating whether U.S. President Donald Trump's first national security adviser, Michael Flynn, was involved in an alleged plan to seize a Muslim cleric and deliver him to Turkey in exchange for millions of dollars, the Wall Street Journal reported on Friday. Gulen has denied Erdogan's claims.
The Journal reports that federal authorities have asked at least four people about a meeting at the 21 Club in New York City in mid-December, after Trump's victory but before he took office in January.
The kidnapping and return of Gulen would have netted Flynn and his son, Michael Flynn Jr. Former CIA Director James Woolsey said in March that he had attended a meeting with Flynn and Turkish government ministers in which the removal of Gülen outside of the US extradition process was "hypothetically" discussed. Former CIA director James Woolsey earlier told media that Flynn met with Turkish government officials in September 2016 to forcedly send Gulen back to Turkey.More news: UCLA players arrested in China still waiting for official investigation
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. Flynn then retroactively registered as a foreign agent.
Flynn is already being investigated as part of Mueller's probe into Russian interference in the 2016 election. In his resignation letter he apologized to the president for giving "incomplete information" about his interactions with the Russian ambassador to the U.S.
The December meeting about Gulen was also reported Friday by NBC, which cited people familiar with the probe.
It is unclear how Flynn, as national security adviser, could have successfully carried out either alleged request.
Investigators also are looking into what possible role Flynn's son, Michael G. Flynn, may have played in any such efforts. Flynn penned an op-ed last November suggesting the US should expel Gulen.
Barry Coburn, a lawyer for Mr Flynn's son, told the BBC he had no comment on the report.