Turkey has detained a nephew of US-based preacher Fethullah Gulen after last week's failed coup, state-run media reported on Saturday, the first time one of his relatives has been apprehended in the current crackdown.Muhammet Sait Gulen will be taken to the capital Ankara after he was detained in Erzurum, the eastern region where his 75-year-old uncle is said to have developed his deep convictions, close to his birthplace of Korucuk.Erzurum is thought to be home to many Gulen supporters and members of his Hizmet movement, which Turkish authorities say was behind the bloody attempted power grab on July 15.Gulen, the Pennsylvania-based arch-foe of President Recep Tayyip Erdogan, is accused of "masterminding" the putsch through his movement, a claim he strongly denies.The nephew was detained in connection with the coup, which Turkey says was organised by the "Fethullah Terrorist Organisation", state-run news agency Anadolu reported.Anadolu said he was also wanted over the leak of questions from 2010 civil service exams.In May this year, another nephew of the former imam in self-imposed exile was detained in connection with schools run by the movement, according to a state media report at the time.In Erzincan, another province believed to be home to many Gulenists, an investigation was launched on Saturday into 263 civil servants while 45 people were arrested, Anadolu reported.Followers of Gulen have held prominent positions in Turkey's security and civil services, media and business -- although less so after purges of recent years. Tens of thousands of people have been detained, sacked or suspended in the wake of the failed coup.