In total, 251 died and more than 2,200 were wounded resisting rogue military units in the attempted coup.
Turkey said on Thursday it had uncovered a mass grave containing dozens of bodies in a Turkish-held region of northern Syria, accusing a US-backed Kurdish fighter group of the killings.
Turkey and its Syrian proxies have seized control of territory inside Syria since 2016 in military operations against ISIL (ISIS) and the YPG Kurdish group.
The governor of Turkey’s Hatay province on the border with Syria told reporters a mass grave was found with 61 bodies in the Afrin area.
“This is a crime against humanity,” Rahmi Dogan said, blaming the YPG, which is backed by Washington.
“I think the number of bodies recovered will rise,” he added, after the Turkish defence ministry initially put the number at 35 on Wednesday.
Images on Turkish television showed officials in hazmat suits surrounded by what appeared to be bodies in bags.
Dogan said Turkish authorities believe the dead were civilians executed by the YPG days before Turkey launched its so-called Olive Branch operation in 2018 to capture Afrin.
Turkey’s President Recep Tayyip Erdogan had said at the time that the operation in Afrin would be followed by a push into the northern town of Manbij, which the US-backed Kurdish forces captured from ISIL in 2016.
AFP was unable to independently verify the claims.
The YPG has so far not commented on the allegations.
Turkey accuses the YPG – a force backed by Western militaries against ISIL – of being a “terrorist” offshoot of the outlawed Kurdistan Workers Party (PKK).
Turkey has been battling armed Kurdish fighters for decades in the southeastern part of the country. Among those groups Ankara is fighting is the Kurdistan Workers Party, or PKK, which had separatist roots, and later pushed for more autonomy from the Turkish central government.
The violence has left 40,000 civilians, soldiers and armed fighters dead, costing the country hundreds of billions of dollars.
Turkey along with the European Union and the United States consider the PKK a “terrorist organisation”.