Washington (CNN) Former White House national security adviser Mike Flynn and his son are alleged to have been offered as much as $15 million to forcibly remove from the US a Muslim cleric wanted by Turkey, The Wall Street Journal reports .

The Journal reported the FBI questioned at least four people in regards to a mid-December meeting in New York at the "21" Club. Discussions between Flynn and Turkish representatives supposedly took place there, according to the Journal.

The Journal said the people who described the alleged proposal didn't attend the December meeting and didn't have direct knowledge of the details. There's no indication that money changed hands or that an agreement was made.

The discussions allegedly included how to transport Fethullah Gulen, a Muslim leader who Erdogan has accused of being behind a failed military coup to overthrow him, on a private jet to the Turkish prison island of Imrali.

Flynn's lawyers fully denied the Journal story in a written statement later Friday.

"Out of respect for the process of the various investigations regarding the 2016 campaign, we have intentionally avoided responding to every rumor or allegation raised in the media," Robert Kelner, Stephen Anthony and Brian Smith said in the statement. "But today's news cycle has brought allegations about General Flynn, ranging from kidnapping to bribery, that are so outrageous and prejudicial that we are making an exception to our usual rule: they are false."

The Journal reported that an attorney for Flynn's son declined to comment on the story.

The Turkish embassy denied in a statement Saturday that it would "resort to means external to the rule of law for (Gulen's) extradition" and said such claims are "utterly false, ludicrous and groundless."

CNN reported earlier this week that special counsel Robert Mueller's investigators are examining Flynn's alleged participation in discussions about the idea of removing the cleric who has been living in exile in Pennsylvania. In the past, a spokesman for Flynn has denied that such discussions occurred.

CNN also reported that Flynn has expressed concern about the potential legal exposure of his son, Michael Flynn Jr., who, like his father, is under scrutiny by Mueller, multiple sources familiar with the matter tell CNN.

Former CIA Director James Woolsey told CNN in March about an earlier meeting in September 2016 where Flynn also met with representatives of the Turkish government and discussed potential ways to send a foe of Turkey's president back to face charges in that country.

Woolsey claims that those present discussed sending Gulen back to Turkey to face charges -- possibly outside the legal US extradition system.

"What I saw and heard was sort of the end of the conversation -- it's not entirely clear what transpired because of that," Woolsey said on "CNN Tonight" with Don Lemon. "But it looks as if there was at least some strong suggestion by one or more of the Americans present at the meeting that we would be able, the United States would be able, through them, to be able to get hold of Gulen, the rival for Turkey's political situation."

At the time, a spokesman for Flynn denied the allegation.

"The claim made by Mr. Woolsey that General Flynn, or anyone else in attendance, discussed physical removal of Mr. Gulen from the United States during a meeting with Turkish officials in New York is false," Flynn spokesman Price Floyd said in a statement at the time. "No such discussion occurred. Nor did Mr. Woolsey ever inform General Flynn that he had any concerns whatsoever regarding the meeting either before he chose to attend or afterwards."

If proven, the alleged plan to kidnap the cleric with the aid of foreign money directly violates US criminal code and could result in up to a 20-year sentence for the Flynns, according to Michael Zeldin, a CNN legal analyst.

"Under this statute, both domestic kidnapping in violation of US law, and if it was a crime in Turkish law, both would be specific unlawful activities, so anyone who engages in the effort to bring money into the US for the purpose of kidnapping another violates the statute. That's a 20-year felony," Zeldin said.

If the cleric were to die once in Turkish hands, that could mean a life sentence for the pair, Zeldin said.

"This probably has nothing to do with the Trumps, but this is a very serious crime," he said. "Theoretically, if they did this international kidnapping and the Turkish government killed this guy, that could be a life sentence for the Flynns. You don't really want to be involved in a scheme like this, no matter how broke you might be."

The Mueller investigation into the Flynns is part of an overall probe into the Trump campaign's involvement with Russia.

Flynn is also under legal scrutiny by Mueller's team for undisclosed lobbying that he did during the presidential campaign on behalf of the Turkish government, according to sources familiar with the matter. It's against the law to lobby in the United States on behalf of a foreign government without informing the Justice Department.