At least 45 people, including five children, were killed in southern Syria as the army launched an all-out assault on two towns in Daraa province, according to the Syrian Observatory for Human Rights.
"The number of people killed by gunfire, shelling, summary executions and clashes pitting rebels against troops on Wednesday in the towns of Al-Sanamein and Ghabagheb has risen to 45," the watchdog has stated.
There was no immediate comment from Syrian state officials.
Security forces had been fighting anti-Assad rebels in the town in Deraa, a province bordering Jordan that has become a focal point of battles as both sides seek to control Syria's frontiers and seize supply lines to the capital, Damascus.
The crisis in Syria is expected to be high on the agenda when foreign ministers from the G8 group of nations hold talks in London on Thursday.