BEIRUT, Lebanon — Five rescue workers with a civil defense group were killed in aerial attacks on their headquarters in northern Syria on Tuesday as violence escalated in the critical battlegrounds of Aleppo Province, where government and insurgent attacks have killed dozens in recent days.

The rescuers died after four airstrikes and a surface-to-surface missile hit the headquarters in quick succession in Atareb, in western Aleppo Province, according to the group, the White Helmets, a civilian organization that responds to attacks in insurgent-held territory and says it has helped save as many as 50,000 people. Airstrikes in the area are being carried out by the government and its Russian allies.

A day earlier, 19 civilians, including several children, were killed by insurgent shelling in the government-held section of the divided city of Aleppo, according to the state-run news media. Opposition groups and news outlets put the death toll from government airstrikes and shelling over the past week at well over 100.

The rash of attacks was an indication that a partial truce that held for nearly two months had collapsed, with dire results for Syrians in both government-held and rebel-held territory. Areas held by the extremist Islamic State group were not included in the truce.