* Rebels, Nusra Front powerful in southern Syria
* Hezbollah helps army in offensive - monitor, source
* Syria voices criticism of Jordanian support for rebels
By Oliver Holmes
BEIRUT, Feb 10 (Reuters) - Syria's army gained ground from rebels in the south on Tuesday in what a monitoring group described as a large-scale offensive in the region backed by Lebanese Hezbollah fighters against insurgents including al Qaeda's Syrian wing.
The south is one of the last remaining areas where mainstream, non-jihadist rebels fighting President Bashar al-Assad have a foothold. Just a short drive to Damascus, the area remains a risk to the Syrian leader, who has otherwise consolidated control over much of the west.
"The operation started two days ago and is very big," Rami Abdulrahman, head of the Syrian Observatory for Human Rights monitoring group, said on Tuesday.
Abdulrahman said the offensive aims to take a triangle of rebel-held territory from rural areas southwest of Damascus to Deraa city to Quneitra. Syrian media and rebel sources said on Tuesday that battles raged in several areas of southern Syria.
Syrian troops had been on the defensive in the south, losing control of large areas of countryside near Jordan as well as parts of the border along with Israel near the Golan Heights, according to regional military analysts and diplomats.
The southern rebels, often described as the best organised of the mainstream armed opposition, see themselves as the last hope for a four-year-old uprising and civil war hijacked by Islamist militants, and are seeking a higher profile and more help.
But the Nusra Front, al Qaeda's Syrian wing, also has a presence in the region. Sunni Islamist insurgents also control wide expanses of Syria's north and east.
Hezbollah's al-Manar news channel said government forces had captured the town of Deir al-Adas and Syrian state television quoted a military source saying the town of Denaji between Damascus and the far southern boundary town of Quneitra was taken "a number of terrorists were eliminated".
The leader of a mainstream rebel group in the area said the situation in Deir al-Adas was "dangerous" and that the nearby town of Deir Maker had fallen to government forces.
Syria's state news agency SANA said the army had also killed insurgents near the town of Sheikh Maskeen, close to the main north-south highway between Damascus and the Jordanian border.
A mainstream rebel group in southern Syria calling itself "The First Army" said in a statement that it had started a battle to take control of Namer and Qarfa in Deraa province and would attack six other locations. It also declared the main highway leading to Damascus as a military zone.
A reporter for the Lebanese al-Mayadeen news channel, which has embedded its journalists with the Syrian army, said from Quneitra that the large-scale army operation had cut off an important supply route for rebels from Jordan to rebel-controlled areas west of Damascus.
The mainstream rebel groups known collectively as "The Southern Front" have received support from states that oppose Assad. That aid, some of it military, has been channelled through Jordan, a staunch ally of the United States and Gulf Arab monarchies that have taken a strong position against Assad. (Additional reporting by Tom Perry; Editing by Mark Heinrich)
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