Turkish police arrested more than 20 people on charges of "terrorist propaganda" on Thursday over their criticism of a military offensive launched against Kurdish forces in Syria.
The head of opposition news site Birgun, Hakan Demir, was detained for "inciting the people to hatred and enmity" after it reported there had been civilian casualties in the offensive, which was launched on Wednesday.
The government denied civilians had been hurt in its strikes on Kurdish militant positions in northern Syria.
Demir was later released but had his passport confiscated.
Police arrested 21 people in the Kurdish-majority city of Mardin in southeastern Turkey for "terrorist propaganda", according to state news agency Anadolu.
They had already announced that 78 cases had been opened against individuals nationwide.
Meanwhile, Ankara's chief prosecutor said cases had also been opened against the leaders of the pro-Kurdish Peoples' Democratic Party (HDP), Sezai Temelli and Pervin Buldan, and other members of the party.
They had described the military operation as "an invasion" in a statement, and Temelli maintained his position on Thursday, saying it was an act of "aggression" and "attempted occupation".
Turkey launched "Operation Peace Spring" on Wednesday against the Kurdish-led Syrian Democratic Forces, which it considers a "terrorist" offshoot of Kurdish insurgents in its own territory.
Criticism of military operations in Turkey is fiercely taboo, with even opposition parties required to praise them.
Turkey arrested online critics during previous offensives against Kurdish forces in Syria, accusing them of "terrorist propaganda".
Rights groups criticise the erosion of free speech under President Recep Tayyip Erdogan, particularly in the wake of a failed coup in 2016 which was followed by tens of thousands of arrests of political opponents.