Opposition activists said Syrian troops backed by Lebanese Hezbollah fighters were pressing a sustained assault on Qusair, a town long used by insurgents as a way station for arms and other supplies from Lebanon.

For Assad, Qusair is a crucial link between Damascus and loyalist strongholds on the Mediterranean coast. Recapturing the town, in central Homs province, could also sever connections between rebel-held areas in the north and south of Syria…

In Harasta, an eastern Damascus suburb largely under rebel control, dozens of people were afflicted by respiratory difficulties after an apparent overnight chemical attack, according to opposition sources. Video showed victims lying on the floor of a room, breathing from oxygen masks.