Enes Kanter, a Turkish citizen who is a six-year veteran of the N.B.A., found himself in an apparent political tussle on Saturday that began at a Romanian airport and ended hours later, in London, with Kanter proclaiming on Twitter that he would continue on to New York to hold a news conference on Sunday with “lots of things to say.”
What he seems certain to talk about is his outspoken opposition to Turkey’s president, Recep Tayyip Erdogan, and how that stance seemed to have led to Saturday’s chain of events, in which the N.B.A. ultimately asked for the State Department’s help in assisting Kanter.
The day started with Kanter, a 6-foot-11 center for the Oklahoma City Thunder, saying in a video posted on Twitter that he had been detained at the Bucharest airport, with the authorities telling him that his passport had been canceled.
Kanter said his political opposition to Turkey’s president was the reason for the detention. Hours later, the Romanian authorities said he was free to go.
In an interview with The New York Times, Fabian Badila, a spokesman for the Romanian border police, said Kanter had arrived in Romania on a flight from Frankfurt at about 1 p.m. on Saturday.
“My colleagues established that his travel documents weren’t valid,” Badila said, “that they had been canceled by his home country, so he wasn’t allowed to enter the country.”
Badila added, in reference to Kanter: “At around 5 p.m., he left the airport on a flight to London. While he was at the airport, he wasn’t detained or locked up; he was allowed to wander around, but he couldn’t enter the country.”
Later on Saturday, Kanter posted a message on Twitter saying that he was safe in London, with New York his next stop. “Got lots of things to say with lots of crazy stories,” he wrote.
The N.B.A. said it had worked with the State Department to ensure Kanter’s release in Romania.
As to the status of his passport, and why he was allowed to travel to London without a valid one, no official announcements have been made. But in an interview with The Oklahoman, Hadis Fetic, an executive assistant for Kanter, said that the Turkish government has been known to report citizens’ passports as stolen or missing in order to have them confiscated in foreign countries and that Fetic believes that is what happened with Kanter’s passport.
The detention occurred while Kanter, who turned 25 on Saturday, was in the midst of a tour for his Enes Kanter Light Foundation.
“The reason behind it is, of course, my political views,” Kanter said in the video.
“You guys know him by, you know, he has attacked the people in Washington,” Kanter said, referring to a recent episode involving Erdogan’s bodyguards and protesters in Washington. “He is a bad, bad man; he is a dictator, and he is the Hitler of our century.”
Kanter is known to support Fethullah Gulen, an Islamic cleric based in the United States whom Erdogan has accused of orchestrating last year’s failed coup attempt in Turkey.
If Kanter had been deported to Turkey on Saturday rather than being allowed to continue his travels, he could have faced serious difficulties. Since the failed coup, the Turkish authorities have arrested thousands of people thought to be supporters of Gulen.
Along with the video, Kanter posted two photos of himself with officers holding him at the Bucharest airport. In English, he just wrote “#FreeEnes”; in Turkish, he wrote: “Haha, the police officers guarding us are taking pictures. Who do you think you are messing with you cowards.”
This was not the first time that Kanter had problems apparently related to his outspoken views about the Turkish president. It was reported last July that he had received death threats after he criticized the government after a terrorist attack in Turkey. He posted screenshots on Twitter of messages he had received with phrases like “You will die soon” and violent imagery.
Last August, Kanter’s father, Mehmet, publicly condemned his son’s political views, writing a letter published by the Turkish news media that claimed his son had been hypnotized by Gulen.
“With a feeling of shame I apologize to our president and the Turkish people for having such a son,” Mehmet Kanter wrote.
Enes Kanter, who was born in Switzerland, is one of Turkey’s most famous athletes. He has said his political views resulted in his being left off the Turkish national basketball team for EuroBasket 2015. The team’s coach, Ergin Ataman, denied the accusation.
Kanter has been with the Thunder since a trade during the 2014-15 season. His college career at Kentucky was aborted when the N.C.A.A. ruled him permanently ineligible because he had been paid by a club in Europe before enrolling at the university.
Kanter’s day on social media started with his retweeting the N.B.A. wishing him a happy birthday, but within an hour of that message he was posting photos of the incident at the airport.
Correction: May 20, 2017
An earlier version of the summary with this article misstated Enes Kanter’s nationality. He is a Swiss-born Turkish citizen, not a native of Turkey.