Kanter had arrived in Bucharest from Jakarta, Indonesia as part of his 2017 Enes Kanter Light Foundation global tour. The Thunder are working with the NBA office and gathering information about the ongoing situation, according to ESPN.
Kanter has long been at odds with the Turkish government, and is a strong critic of its current president, Recep Tayyip Erdogan. He is a supporter of Fethullah Gulen, a former imam living in self-imposed exile in the United States, whom Erdogan has accused of orchestrating the failed coup in Turkey last July.
Kanter has faced severe backlash in his home country for his views, including being publicly disowned by his father, who last August wrote: "I apologize to the Turkish people and the president for having such a son."
Kanter says Erdogan - who recently expanded his executive powers via a referendum - is personally responsible for stripping him of his passport.
"He's a dictator," Kanter said.
Saturday, incidentally, is Kanter's 25th birthday.