ANKARA, Turkey (AP) — Turkey's state-run news agency says police have detained a prominent investigative journalist for questioning over a series of social media postings.

Anadolu Agency said Thursday Ahmet Sik was detained on suspicion that he insulted the state, its military and police and engaged in terrorist propaganda on Twitter.

Arrests and prosecutions of writers and journalists have added to concerns over the deteriorating state of rights and freedoms in Turkey.

His arrest comes as novelist Asli Erdogan and other employees of a pro-Kurdish newspaper were due to appear in court over charges of supporting outlawed Kurdish rebels.

Turkish authorities have arrested 1,656 people in the past six months for allegedly supporting terrorist organizations or insulting officials on social media, and is investigating another 10,000 people, according to government figures.