ISTANBUL (Reuters) - Turkish police began an operation to detain 121 former foreign ministry staff across the country on Thursday over their alleged links to the U.S.-based cleric who Ankara says orchestrated last year’s attempted coup, state-run Anadolu agency said.

It said the ministry personnel were previously dismissed over suspected ties to Islamic preacher Fethullah Gulen, who lives in self-imposed exile in Pennsylvania. He has denied involvement in the failed putsch in July 2016.

Counter-terrorism police squads began simultaneous raids in 30 provinces to capture the suspects, some of whom were believed to be users of ByLock, an encrypted messaging app which the government says was used by Gulen’s network, Anadolu reported.

Under a crackdown since the coup, more than 50,000 people have been jailed pending trial over alleged links to Gulen, while 150,000 people have been sacked or suspended from jobs in the military, public and private sectors.

The government dismisses rights groups’ concerns about the crackdown, saying only such a purge could neutralize the threat represented by Gulen’s network, which it says infiltrated institutions such as the judiciary, army and schools.