Syrian rebels advancing from the Jordanian border seized a strategic army position in the southern city of Daraa on Friday as fighting raged in the surrounding province, a watchdog said.
"They seized two buildings in the provincial capital that regime forces were using to keep the whole city under surveillance," Syrian Observatory for Human Rights director Rami Abdel Rahman said.
"This is the most important army position that the rebels have seized in Daraa" in 27 months of conflict, he told AFP.
"The province could act as a key conduit for arms to stream in from Jordan to rebels in Damascus province," Abdel Rahman added.
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The Los Angeles Times reported last week that US special forces were providing training in Jordan to Syrian rebels, including instruction in the use of anti-tank and anti-aircraft weapons.
Officials in Amman denied the report, which came as Washington said it was to begin delivering arms to the rebels.
The rebel advance came as the army stepped up its shelling of rebel-held areas of Daraa province, killing at least six women and four children, the Observatory said.
It also came after five people were killed in a bomb attack in a mainly Christian neighbourhood in central Damascus on Thursday, the Observatory said, revising an earlier claim the explosion was caused by a suicide bomber.
At least 115 people were killed on Thursday in violence in Syria, the Observatory said.
In 27 months, more than 100,000 people have died in the conflict, which morphed from a popular movement for change into an insurgency after the regime unleashed a brutal crackdown on dissent.