Fethullah Gulen, the Muslim cleric and bitter foe of Turkish President Recep Tayyip Erdogan, Monday dismissed as doomed to fail Ankara's bid to extradite him from the United States over a failed coup attempt.

Gulen, the spiritual leader of the Hizmet movement -- which promotes moderate Islam across dozens of countries and is dubbed a terrorist group by Erdogan -- firmly denies Ankara's charge he was behind the coup bid.

"I have no concerns personally," Gulen said in an interview with several media outlets including AFP at his compound in the Pennsylvania town of Saylorsburg he has called home since 1999 under self-imposed exile.

The United States "is a country of law," added the cleric.

"The rule of law reigns supreme here. I don't believe this government will pay attention to anything that is not legally sound.

"As a side note, I will die one day. Whether I die in my bed or in prison, I don't care," said Gulen, 75.

Erdogan told CNN a formal request for the extradition of the 75-year-old Gulen would be submitted in the coming days.

But US Secretary of State John Kerry said Ankara would need to provide "evidence, not allegations" against Gulen.

The Turkish government previously sought -- unsuccessfully -- to extradite Gulen after the corruption scandal that shook the country in 2013 and triggered the resignation of three ministers.

"Because those were not legal demands, the US government did not pay attention, did not take them seriously," Gulen said.

"They were not acceptable, reasonable and legal requests... Now through this attempted coup, it looks like they have strengthened their hands. They will attempt to do the same thing."

- Turkey needs US more -
Gulen, who members of his circle say suffers from diabetes and cardiovascular disease, was visibly tired.

While he may not be concerned about his own fate, the opposition leader said he was very worried about worsening relations between the United States and key NATO ally Turkey.

He recalled that Turkish troops fought alongside their American counterparts during the Korean War, and that the two nations have been close allies for decades at the transatlantic military alliance that Turkey joined in 1952.

"If it is separated from NATO, Turkey would go into a chaos of problems. It would evaporate itself. It would really finish itself," Gulen said.

"The United States could find other options, but I think Turkey needs the United States' partnership more than the US needs Turkish partnership."

Turkey has sacked almost 9,000 officials in its relentless crackdown against suspected plotters of the coup attempt, which killed more than 300 people.