Fethullah Gulen, the Islamic preacher who was a major ally of President Recep Tayyip Erdogan of Turkey before being accused of plotting a failed coup against him in 2016, has died. He was 83.

Mr. Gulen died late Sunday in a hospital in the United States, where he had lived in self-imposed exile since 1999, according to the social media account of Herkul, a website that posted his sermons. It did not mention a cause of death.

During his own rise as an Islamist in a staunchly secular country, Mr. Erdogan found useful political allies in Mr. Gulen’s followers. But the two men later had a falling out, and in 2016 the Turkish government designated the Islamic movement founded by Mr. Gulen as a terrorist organization.

Mr. Gulen began as a provincial preacher in Turkey and created an international movement called Hizmet, or “service” in Turkish, that ran schools in many countries and promoted a vision of Islam that supported free markets, science and interfaith dialogue.

But his detractors, and indeed enemies, accused his movement of working toward more sinister goals. For more than a decade, his followers, known as Gulenists, worked closely with Mr. Erdogan’s ruling Justice and Development Party, angering Turks who said the two Islamist groups were working together to erode the foundations of Turkey’s secular republic.

Mr. Erdogan’s political alliance with the Gulenists began to break down about a decade ago, finally shattering after the 2016 coup attempt. About 250 people had been killed by the time the Turkish government shut down the rebellion.

Mr. Erdogan held Mr. Gulen responsible for the failed coup and began a vast purge in its aftermath, imposing a state of emergency for two years, detaining 100,000 people and purging 150,000 public employees from their jobs. More than 8,000 military personnel were prosecuted on charges of complicity in the insurrection.

The crackdown shuttered Gulenist schools and newspapers in Turkey and effectively destroyed the movement as an overt force in Turkish society and politics. Many of its prominent figures went into exile.

Mr. Gulen denied that his group had anything to do with the attempted coup and lived a largely reclusive life in Pennsylvania, a fact that fueled frequent but unproven accusations from Mr. Erdogan and other Turkish officials that the preacher was an American asset who had been deployed to weaken Turkey.