ISTANBUL—Turkey’s state-run news agency says a court has accepted an indictment against columnists and senior staff from the opposition Cumhuriyet newspaper for “aiding terrorist organizations.”

Anadolu Agency said Tuesday the 274-page indictment accused 19 people of “sponsoring” several outlawed organizations, including Kurdish militants, a far-left group and the network of U.S.-based cleric Fethullah Gulen, who is blamed for last summer’s failed coup.

Twelve of the suspects, including investigative journalist Ahmet Sik, columnist Kadri Gursel and cartoonist Musa Kart, have been in pretrial detention for months. Anadolu said two suspects are being sought.

The arrests are part of a widespread crackdown in the wake of the attempted coup, which has led to the imprisonment of more than 40,000 people. The Committee to Protect Journalists says Turkey has the highest number of imprisoned journalists in the world.

The first hearing is scheduled for July 24.