At least 21 Turkish-backed Syrian opposition rebels were killed while combing an area previously controlled by the Islamic State terrorist militia in north-eastern Aleppo province, a monitoring group said Monday.
"While rebels were combing the Turkman Barih village on Sunday, landmines planted by the Jihadist movement exploded, also wounding 29 other rebel fighters," the Britain-based Syrian Observatory for Human Rights said.
However, local Turkish media quoted an army statement as saying "clashes in northern Syria have killed 15 Ankara-backed Free Syrian Army (FSA) fighters in the last 24 hours."
This is the largest death toll inflicted among the ranks of the rebels since they started their offensive backed by the Turkish army and planes against Islamic State near the Turkish-Syrian border on August 24.
The incident prompted the rebels to withdraw from the area they had managed to take control of on Sunday, located 13 kilometres south-west of the strategic border town of al-Rai.
Al-Rai is one of the centres of Turkey's recent ground intervention in support of Syrian rebels against Islamic State and Kurdish-led forces.
The Islamist State extremist group used the area, north-east of Aleppo, to bring foreign fighters into its territories in Iraq and Syria.