The Syrian Observatory for Human Rights said the toll was the highest loss of life for forces involved in the Turkish-led operation in northern Syria since it began in late August.
The Britain-based monitor said 21 rebels were killed and dozens more wounded, many seriously, while attempting to secure the village of Turkman Barah, near the flashpoint IS-held town of Dabiq in Aleppo province yesterday.
Turkish troops were not mentioned among the casualties.
The jihadist group has regularly laid mines and booby-trapped buildings with explosives as it withdraws under attack.
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Abdel Rahman said the toll prompted the rebel forces to redeploy outside Turkman Barah.
Turkey began its unprecedented operation inside Syria, dubbed Operation Euphrates Shield, on August 24.
Ankara says it is targeting IS but also Kurdish fighters from the People's Protection Units (YPG), which Turkey considers to be a "terrorist" group.
The YPG has been a key ally of the US-led coalition fighting IS and has seized large swathes of territory from the jihadist group, raising concerns in Ankara about the creation of a contiguous semi-autonomous Kurdish region along the Syria-Turkey border.
The Turkish-backed Syrian rebels have this month pushed towards Dabiq, which holds symbolic importance for IS because of a Sunni prophecy that states it will be the site of an end-of-times battle between Christian forces and Muslims.
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