BEIRUT, Lebanon — In Aleppo, there are again reports of dead children. In Damascus, clashes reverberate close to downtown.

Across Syria, airstrikes are inching back into the realm of the expected, and the United States acknowledged on Saturday that its warplanes had inadvertently bombed Syrian government troops.

After less than a week, the partial cease-fire declared by Russia and the United States is fraying. Help has still not reached those who need it most, despite promises at the start of the truce that the government would allow aid convoys to travel.