ISTANBUL (Reuters) - Turkish prosecutors have issued detention warrants for 117 military personnel over alleged links to the U.S.-based cleric accused by Ankara of orchestrating last year’s attempted coup, security sources said on Friday.

They said counter terrorism police in the western province of Izmir launched an operation early on Friday to detain the military staff, some of whom served in key units of the armed forces.

Turkey says supporters of Islamic preacher Fethullah Gulen, who has lived in self-imposed exile in the United States since 1999, were behind the abortive putsch in which 250 people were killed. He has denied involvement.

The personnel facing arrest had been in phone contact with senior members of the cleric’s movement between 2010 and July 15 last year when the coup was launched, the sources said.

Since then more than 50,000 people have been jailed pending trial over links to Gulen, while 150,000 people have been sacked or suspended from jobs in the public and private sectors for the same reason.

Rights groups and some of Turkey’s Western allies have voiced concern about the crackdown, fearing the government is using the coup as a pretext to quash dissent.

The government argues that only a massive purge could neutralize the threat represented by Gulen’s network, which it says deeply infiltrated Turkey’s institutions - the army, schools and courts.