U.S. President-elect Donald Trump's choice to be national security adviser has suggested that Washington should improve its relations with Turkey by extraditing a cleric whom Ankara blames for a coup attempt in July.

Retired Lieutenant General Michael Flynn, the former director of the Defense Intelligence Agency whose appointment was announced on November 18, described Fethullah Gulen on his blog site for The Hill newspaper as "a shady Islamic mullah residing in Pennsylvania" who is hiding a "radical Islamist" agenda.

"Gulen's vast global network has all the right markings to fit the description of a dangerous sleeper terror network. From Turkey's point of view, Washington is harboring Turkey's Osama bin Laden," Flynn wrote on election day. "We should not provide him safe haven."

Flynn noted that Gulen followers have been donors to the Clinton Foundation, a global charity headed by the family of Trump's Democratic rival Hillary Clinton.

"It is time we take a fresh look at the importance of Turkey," he wrote. "We need to adjust our foreign policy to recognize Turkey as a priority. We need to see the world from Turkey's perspective."

In light of Flynn's comments, Turkish President Recep Tayyip Erdogan hailed Trump's victory as a "new era" in Ankara's relations with Washington and has stepped up demands that Gulen be immediately handed over since the November 8 election.

The Obama White House, to Erdogan's frustration, has said it will let the Justice Department decide whether there is any legal merit in Turkey's extradition request in what likely would be a long, bureaucratic process.

Gulen has never been charged with a crime in the United States, and he has consistently denounced terrorism, as well as the failed coup in Turkey, as have the schools and charitable organizations associated with him.

One of Gulen's lawyers, Jason Weinstein, called Flynn's comments about Gulen "troubling," but expressed confidence that the United States will continue to handle the matter fairly.

"We hope and expect that the law will be followed here and that politics will not interfere with the judgment of career officials at [the Justice Department]. If the law is followed, then we are confident that Mr. Gulen will not be returned to Turkey, where he is certain to be subject to torture, a sham trial, and execution," Weinstein said.

With reporting by AP, dpa, and TASS