Secretary of State John Kerry is calling on Turkey to provide hard evidence that a U.S.-based cleric was behind a foiled coup attempt last weekend if it wants him extradited.

Kerry said Wednesday that mere allegations of wrongdoing against Fethullah Gulen would not meet U.S. extradition requirements. Kerry said he had made that clear in several phone calls with Turkey's foreign minister in recent days.

Turkey submitted documents about Gulen, who lives in exile in Pennsylvania, to the Justice Department on Tuesday. U.S. officials have not yet said whether they constitute a formal extradition request.

Kerry also said Turkish officials have said that power to the Incirlik Air Base that was cut off in the aftermath of the coup would be restored in the next two days.