The rebel-held Qusair is home to about 20,000 residents and has been besieged for weeks by government troops. Opposition activists say members of the Lebanese militant Hezbollah group are also fighting with President Bashar Assad's troops in the area.
The Britain-based Syrian Observatory for Human Rights says 16 people were killed Sunday in Qusair but that the death toll is expected to rise.
The town is strategically important because it links Damascus with the coast, where regime loyalists are concentrated. This includes Alawites, followers of a Shiite offshoot to which the Assad family belongs. The rebellion against Assad is largely driven by Syria's majority Sunnis.
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