Fethullah Gülen, leader of Hizmet movement accused of 2016 ...

US-based cleric Fethullah Gülen, who built a powerful Islamic movement in Türkiye and beyond but spent his later years mired in accusations of orchestrating an attempted coup, has died aged 83.

Gülen died on Sunday in a United States hospital where he was being treated, Herkul, a website which publishes his sermons, said on X.

He had lived in the US in self-imposed exile since 1999.

Turkish President Tayyip Erdoğan held Gülen responsible for the 2016 attempted coup against him, in which rogue soldiers commandeered warplanes, tanks and helicopters. Some 250 people were killed in the bid to seize power.

Gülen denied involvement in the coup attempt, but his movement was designated a terrorist group by Türkiye.

Turkish Foreign Minister Hakan Fidan confirmed Gülen's death, describing him as the leader of a "dark organisation".

"Our nation's determination in the fight against terrorism will continue, and this news of his death will never lead us to complacency," he told a press conference.

Mr Fidan said he hoped Gülen's death would lift a "spell" over Turkish youth who had taken a path of "betrayal" against their country under the pretence of religious values.

According to its followers, Gülen's movement — known as "Hizmet" (meaning "service" in Turkish) — seeks to spread a moderate brand of Islam that promotes Western-style education, free markets and interfaith communication.

Since the failed coup, his movement has been systematically dismantled in Türkiye and its international influence has declined.

Tayyip Erdoğan was Gülen's one-time ally.   (Reuters: Zorana Jevtic)

Known to his supporters as Hodjaefendi, or respected teacher, Gülen was born in a village in the eastern Turkish province of Erzurum in 1941. 

The son of an imam, or Islamic preacher, he studied the Quran from infancy.

In 1959, Gülen was appointed as a mosque imam in the north-western city of Edirne and came to prominence as a preacher in the 1960s in the western province of Izmir, where he set up student dormitories and would go to tea houses to preach.

These student houses marked the start of an informal network which would spread in coming decades through education, business, media and state institutions.

His influence also spread beyond Türkiye's borders to the Turkic republics of Central Asia, the Balkans, Africa and the West through a network of schools.

Gülen had been a close ally of Mr Erdoğan and his AK Party, but growing tensions in their relationship exploded in December 2013 when corruption investigations targeting ministers and officials close to Mr Erdoğan came to light.

Prosecutors and police from Gülen's Hizmet movement were widely believed to be behind the investigations and an arrest warrant was issued for Gülen in 2014. His movement was designated as a terrorist group two years later.

Soon after the 2016 coup, Mr Erdoğan described Gülen's network as traitors and "like a cancer," vowing to root them out wherever they are. 

Hundreds of schools, companies, media outlets and associations linked to him were shut down and assets seized.

Gülen condemned the coup attempt "in the strongest terms".

"As someone who suffered under multiple military coups during the past five decades, it is especially insulting to be accused of having any link to such an attempt," he said.

In a post-coup crackdown, which the government said targeted Gülen's followers, at least 77,000 people were arrested and 150,000 state workers, including teachers, judges and soldiers, were suspended under emergency rule.

Companies and media outlets regarded as linked to Gülen were seized by the state or closed down. The government said its actions were justified by the gravity of the threat posed to the state by the coup.

Gülen was also reviled by Türkiye's opposition, which saw his network as having conspired over decades to undermine the secular foundations of the republic.

Ankara long sought to have him extradited from the US.

Speaking in his gated compound in Pennsylvania's Pocono Mountains, Gülen said in a 2017 Reuters interview he had no plans to flee the US to avoid extradition.

Even then, he appeared frail, keeping his long-time doctor close at hand.

Reuters