The United States and Turkey are deadlocked over Ankara's demand that Washington extradite Fethullah Gulen, a Muslim cleric it is blaming for the attempted military coup in Turkey, even though he has lived in self-imposed exile in the U.S. for 17 years.
So far, the U.S. is balking at the request.
U.S. Secretary of State John Kerry told Turkey on Monday the U.S. needs "genuine evidence that withstands the standard of scrutiny that exists in many countries" before it would consider extraditing the 75-year-old Gulen, who lives in semi-seclusion in the Poconos Mountains in the northeastern state of Pennsylvania.
The top U.S. diplomat said in Brussels that he told Turkish Foreign Minister Mevlut Cavusoglu "to make certain that in whatever portfolio and request they send us, they send us evidence, not allegations."
Many countries around the world, including the U.S., have treaties with other governments to turn over individuals accused of crimes in foreign lands, but only when there is documented evidence of a crime.
Gulen has denied any connection to last Friday's failed coup, saying, "There is a possibility it could be a staged coup," a pretext for a crackdown on his adherents in Turkey.
Turkish Prime Minister Binali Yildirim remained adamant about Gulen's alleged involvement.
"We would be disappointed if our [American] friends told us to present proof even though members of the assassin organization are trying to destroy an elected government under the directions of that person," Yildirim said. "At this stage, there could even be a questioning of our friendship."
Gulen lives in Saylorsburg, Pennsylvania, on the grounds of the Golden Generation Worship & Retreat Center, an Islamic facility founded by Turkish-Americans. His philosophy mixes a mystical form of Islam with staunch advocacy of democracy, education, science and interfaith dialogue. His movement operates dozens of charter schools in the U.S.
Gulen continues to exert considerable influence in Turkey from 8,000 kilometers away, with supporters in the media, police and judiciary.
Gulen and Turkish President Recep Tayyip Erdogan were once allies, but had a falling out over 2013 corruption investigations in Turkey, which the Turkish leader blamed on Gulen.
The exiled Gulen has also criticized Erdogan's increasingly authoritarian rule, while the Turkish leader has carried out a broad campaign against Gulen's movement in the country, purging civil servants, seizing businesses and closing some media organizations.
The government has accused the 103 generals detained so far for their alleged involvement in the coup attempt of belonging to what the authorities call the Fethullahci Terror Organization, purportedly led by Gulen.