Detained Azerbaijani businessman Reza Zarrab (C) is surrounded by journalists as he arrives at a police center in Istanbul on December 17 ,2013.

The release of a well-connected Turkish-Iranian businessman from federal prison in New York earlier this month could signal a new phase in the ongoing investigation into former White House national security advisor Michael Flynn.

Special Counsel Robert Mueller has expressed interest in a December 2016 meeting between Flynn and representatives of the Turkish government, in which Flynn was reportedly offered $15 million to deliver a political rival of Turkish President Recep Tayyip Erdogan from the United States to Turkey. Flynn denies the allegations and his attorney has called them "outrageous."

According to NBC News, citing three sources, the probe is also investigating whether Flynn discussed ways to free Reza Zarrab, a wealthy gold trader with dual Iranian and Turkish citizenship and personal ties to Erdogan. Zarrab was indicted in 2015 in federal court for allegedly circumventing U.S. sanctions on the Iranian regime by facilitating millions of dollars worth of unlawful transactions. He was set to go on trial in New York later this month.

The Daily Beast reported Thursday that Zarrab was removed from the Metropolitan Correctional Center, a federal facility in New York City, though a spokesperson for the U.S. attorney's office said Zarrab remained in federal custody.

The Bureau of Prisons inmate locator shows that Zarrab was released Nov. 8, three days after NBC News reported that the special counsel had enough evidence to bring charges against Flynn.

A spokesperson for the special counsel declined to comment.