Fethullah Gulen wrote in an article published on Friday in the French daily Le Monde that it was incumbent on Turkey to produce evidence of his guilt before his extradition from his home in the United States.
"If a tenth of the accusations against me are established, I pledge to return to Turkey and serve the heaviest sentence," Gulen wrote in an opinion piece.
Turkey is pressing the US to extradite the 75-year-old cleric and has purged tens of thousands of his suspected followers from the armed forces, other state institutions, the media and academia.
Turkish Foreign Minister Mevlut Cavusoglu told reporters on Friday that Washington might be coming around.
"We have started to receive some positive signals on the calls we have made" for Gulen's extradition, Cavusoglu said, adding that additional evidence was being drawn up to add to the dossier already sent to Washington.
An Islamic cleric with a Green Card
Since 1999, Gulen has lived in self-imposed exile in a rural compound in the US state of Pennsylvania. He is a legal permanent resident of the US.
Turkey has yet to file a formal extradition request. Washington said the US Department of Justice, and then ultimately a court, would weigh the merits of the case once a formal request was made through the appropriate channels.
Turkey's justice minister dismissed the legal procedure as a mere process and said it was a matter of political will in Washington.
"In the end, the decision of the US government will be a political decision," Turkish Justice Minister Bekir Bozdag said in televised remarks. "In a case like this, not to extradite him, of course, would mean to prefer Fethullah Gulen's friendship over Turkey's friendship."
US Secretary of State John Kerry and Vice President Joe Biden expressed their intention to come to Turkey, but they have so far not confirmed a statement from Ankara that the pair would visit on August 24.
jar/msh (AFP, Reuters, dpa)