Turkey has arrested five people over the forced extradition of a defected Syrian army officer.
Authorities announced on Friday that those arrested included Turkish intelligence agents, held "on charges of deprivation of liberty and political spying".
The chief prosecutor in the city of Adana said an investigation had been launched into the forcible return into Syria of Lt Col Hussein Harmoush and another Syrian from the district of Hatay province where they were taking shelter.
Harmoush disappeared from a Turkish refugee camp in August. He had by then become an outspoken leader of the Free Syria Army, a name used by armed resistance groups in neighbouring Syria.
His family claimed that he had been handed over to Syria, but Turkish authorities denied the allegations.
Rights groups reported that he was executed in Syria in January.
Al Jazeera's Anita McNaught said this claim had been questioned.
"His family doesn't believe he's been executed," she said. "But what's certain is that he ended up in Syria against his will."
In September, Harmoush appeared on Syrian state television in what the opposition said was a forced confession, saying "armed gangs" were killing civilians.