The armed forces took control of several villages in the southern province of Daraa in the morning, encircling two other villages where rebel fighters were located, an army statement said.
"This new victory... reopens and secures the vital road between Daraa and Sweida (another southern province) and cuts off the supply route for armed terrorist groups," the statement said.
It called the takeover "a fatal blow" for rebel groups.
Syrian Observatory for Human Rights director Rami Abdel Rahman said government fighters had cut off "a main supply route" that rebels used to bring in fighters and weapons from the Syrian-Jordanian border to their stronghold of Al-Lajjat.
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The military said the town was a "gateway" for opposition fighters and weapons heading north into Damascus province.
Abdel Rahman said that after fierce clashes and heavy regime shelling, pro-government forces captured villages sprinkled around the rebel-held town of Busr al-Harir.
The fighting killed 18 regime force members and 11 rebel fighters, the head of the Britain-based monitoring group told AFP.
In its statement, the army said "the special military operation resulted in the deaths of a high number of takfiri (extremist Sunni) terrorists."
Rebel fighters have gained two significant victories over the army in recent weeks by taking the main border crossing point with Jordan and the ancient town of Bosra al-Sham.
The conflict in Syria has killed more than 220,000 people since it erupted with peaceful protests in Daraa province in March 2011.