Not sure, but this article claims the Syrian regime was responsible...
22 Turkish soldiers confirmed killed in Idlib airstrike as Erdogan chairs emergency meeting on Syria
At least 22 Turkish servicemen have been killed in an airstrike in Syria’s Idlib province, while an unspecified number of soldiers were injured. Turkish officials attributed the strike to the Syrian military.
“In Idlib, Turkey’s armed forces were targeted by the regime elements in an airstrike,” Hatay province Governor Rahmi Dogan told the media late on Thursday. While he originally said that nine soldiers had been killed, minutes later the death toll was revised to 22, the Turkish Anadolu Agency (AA) reported, citing the governor.