BEIRUT — Activists say Syrian warplanes have bombed a building in a suburb of the capital Damascus in the first airstrike since an internationally mediated cease-fire went into effect.

The attack and other violence casts further doubt on the chances that the four-day truce that began Friday will be a springboard for ending the civil war.

The Britain-based Syrian Observatory for Human Rights says eight people were killed and many others wounded in Saturday’s airstrike in Arbeen. The area also has witnessed heavy clashes and intense shelling.

An amateur video posted by activists online shows a pile of rubble said to be from the airstrike. A hand of what appeared to be a dead person could be seen in the debris. The videos appeared consistent with AP’s reporting in the area.