BEIRUT, Lebanon — Anti-government activists in Syria said Tuesday that a chlorine bomb attack by government forces on a northwestern village overnight had killed six people and filled clinics with choking victims.

While the death toll was relatively low, the reports of the attack, in Idlib Province, came less than two weeks after the United Nations Security Council approved a resolution condemning the use of chemicals as weapons in Syria and threatening action in the case of new violations.

Videos posted online showed medics in gas masks dousing victims with water and children lying immobile on hospital beds with foam around their mouths. They also showed what activists said were the remains of two improvised bombs that had been dropped on the village of Sarmeen, in Idlib, late Monday.