ISTANBUL (Reuters) - Turkish prosecutors ordered the arrest of 158 suspects including 33 serving soldiers in an operation targeting people allegedly linked to a Muslim preacher who Turkey says was behind a 2016 failed coup, state-owned Anadolu news agency said on Tuesday.

       The investigation, stretching across 41 provinces, was part of a five-year-old crackdown against the network of U.S.-based cleric Fethullah Gulen. He denies any involvement in the putsch of July 2016, in which more than 250 people were killed.

       So far 97 people have been detained in the latest operation, Anadolu said. The suspects included 110 military students who were expelled in the wake of the coup attempt, as well as 48 serving and former military personnel.

       Following the failed military takeover, about 80,000 people were held pending trial and some 150,000 civil servants, military personnel and others were sacked or suspended. More than 20,000 people have been expelled from the Turkish military.

       (Reporting by Daren Butler; Editing by Lincoln Feast)