Al-Qaeda fighters from the Hurras al-Deen group infiltrated and carried out an attack on a Syrian military base in northern Hama Province on Friday, killing at least 22 troops. This is the highest death toll from a single attack in the area since the Russia-Turkey deal.
Turkey and Russia made the deal specifically to avoid fights between the Islamist groups and the Syrian government. Some al-Qaeda groups have refused to go along with the deal, though Turkey had long insisted they were in compliance by not being in the demilitarized zone separating the two sides.
These jihadist attackers infiltrated across the demilitarized zone to get to the Syrian base, which is likely to further raise questions about the sustainability of the plan, particularly since neither Russia or Turkey were able to prevent the infiltration.
Turkey had insisted on the deal to prevent Syria from invading and ousting the rebels from Idlib Province. This is the last major rebel-held area in Syria, and if such fighting keeps happening, Syria may have a pretext to abandon the deal and attack Idlib outright.