Amnesty International's chairman in Turkey has been arrested on charges of membership of a terror group, the country's official news agency said.
Anadolu news agency reported on Saturday that lawyer Taner Kilic was arrested in the western province of Izmir with five other lawyers who are accused of using an encrypted communication programme.
Kilic was detained on Tuesday and is awaiting trial.
ByLock is allegedly used by the network of US-based cleric Fethullah Gulen, which Turkey blames for orchestrating last summer's coup attempt.
Amnesty International called Kilic's arrest a "devastating injustice". Its secretary general Salil Shetty said the case is proof of Turkey's arbitrary and sweeping crackdown in the aftermath of the failed coup.
More than 50,000 people have been arrested for alleged links to Gulen since last summer.