A brother of US-based Turkish cleric Fethullah Gulen has been detained by police in western Turkey, the state-run Anadolu news agency reports.

Kutbettin Gulen is accused of "membership of an armed terror group", Anadolu said.

He was detained in a raid on the house of a relative in Izmir province, following a tip-off.

Turkey has accused Fethullah Gulen of orchestrating a failed coup in July and has called on the US to extradite him.

He has denied any involvement and has vowed to fight extradition.

The Hurriyet Daily News reported that Kutbettin Gulen had recently arrived from abroad when police, acting on a tip-off, raided the relative's home in the Gaziemir district.

He is now being questioned by anti-terror police.

During the raid, police also confiscated books belonging to Fethullah Gulen, reports added.

Since the failed coup, the government has cracked down on any individuals or groups believed to have links to Fethullah Gulen.

Tens of thousands of people from every level of society have been purged from their jobs, including senior military officers, government officials and school teachers.

Critics of President Recep Tayyip Erdogan say he has used the coup attempt as an way of removing his opponents.

In July police arrested Fethullah Gulen's nephew, Muhammet Sait Gulen, in the eastern city of Erzurum. Another nephew, Ahmet Ramiz Gulen, was arrested in the south-eastern city of Gaziantep in August.