Residents say that tensions in the village, Qalb al-Lawzi, had been raised earlier when Nusra fighters pressured them to convert to Islam, even while other insurgent groups, though allied with Nusra on the battlefield, let them conduct their daily lives and customs.

In the mostly Druse Sweida Province, a different drama was unfolding. Mortar rounds fell on the city of Sweida, sending people fleeing toward Damascus from an area where up to now few have been displaced. Druse in Sweida have largely remained neutral or supportive of the Assad government, but have increasingly resisted sending sons to fight in the army, preferring to keep them home to defend their own areas.

The insurgent offensive was led by the Southern Front, which includes elements that the United States deems sufficiently moderate to receive American aid through a covert C.I.A. program, yet at the same time have often cooperated in battle with Nusra.

By evening, the state news media was declaring that government reinforcements had pushed back the insurgent advance on the air base. And leaders of the Southern Front, seeking to preserve international support and perhaps the backing of locals, had issued statements condemning the Idlib killings as “a crime against Syrian coexistence and the future.”

“We affirm that the people of Sweida are our brothers and our people,” the statement said. “We have not and will not fight them, and we will be with them hand in hand to confront all threats to the province if they ask us to do so.”