Turkish public television said that the preacher, who had lived in Pennsylvania since 1999 and was stripped of his Turkish nationality in 2017, died in hospital.

Gulen's website, Herkul, which is banned in Turkey, said the imam died on "October 20".

Gulen had been an ally of President Recep Tayyip Erdogan.

But after going into exile, Erdogan's government accused his Hizmet organisation of being a "terrorist" group and Gulen of attempting a coup in 2016. He denied the accusations.

Hizmet, which means "service" in Turkish, runs a network of Islamic schools around the world and has become an influential but opaque group.

Gulen allied with Erdogan to help him win elections in the 2000s but became a sworn enemy of the Turkish president after disagreements started in 2010.

Erdogan launched a crackdown on Gulen followers after corruption allegations were made in 2013 against the president's Justice and Development Party.

A failed coup against Erdogan in 2016 deepened the rift.

The president accused Gulen of mounting the coup, 3,000 Gulen followers were given life in jail and legal action was taken against 700,000 people.

About 125,000 government workers, including 24,000 soldiers and thousands of investigating magistrates, were sacked.

News of Gulen's death was widely reported by Turkish media on Monday but the government made no immediate comment.