BEIRUT, Lebanon — For 38 straight days, the streets of the northwestern Syrian town of Maarat al-Noaman had been the scene of protests against the government and the Islamic extremists of the Nusra Front. On Tuesday, they became a scene of carnage, as government warplanes attacked the town’s marketplace, killing dozens of people, according to residents and rescue workers.

The attack confirmed the apparent unraveling of a fragile cease-fire agreement between Syrian government forces and some armed opposition groups. The attack in Maarat al-Noaman, and a similar one in the nearby town of Kafr Nabl, came several days after the start of a new insurgent offensive in a neighboring province, and a day after the main Syrian opposition group said it would no longer participate in diplomatic discussions in Geneva.

The opposition has accused the government of repeatedly violating the partial cease-fire, and Tuesday’s attacks were seen as a violent end to the relative respite from airstrikes that had lasted nearly two months.

Some residents in Maarat al-Noaman, 68 miles north of Homs, and in other towns in Syria that had been afforded a modicum of free space, had resumed the street protests that began the uprising against President Bashar al-Assad more than five years ago. The recent protests have signaled residents’ opposition to the government that has been bombing them and their distaste for extremists fighting among the rebel groups.