Rebels and Islamist forces killed more than two dozen pro-government fighters in a joint attack in a northwestern stronghold of Syrian President Bashar al-Assad's regime, a monitor said on Tuesday.
Government forces backed by Russian air strikes have recovered swathes of southern Deraa province in the last three weeks, advancing unopposed by Assad's western and regional foes into the strategically vital region near Jordan and Israel.
Latest estimates say some 2,000 militants are still holed up in Dara'a city, along with their families.
The campaign in the southwest is now expected to target rebel-held enclaves at the frontier with the Israeli-occupied Golan Heights.
With critical help from Russian Federation and Iran, Assad has now recovered most of Syria.
Syria's civil war has killed more than 350,000 people and displaced millions since it started in 2011 when the regime responded with military force to peaceful protests demanding democratic reforms, triggering an armed rebellion fuelled by mass defections from the Syrian army.
Al Jazeera's Zeina Khodr, reporting from neighbouring Beirut, said the rebel factions in Deraa city agreed to surrender and lay down their weapons overnight.
The government is waging a wide-scale offensive in southern Syria, where it recently retook a major crossing on the border with Jordan.
A suicide vehicle bombing on Tuesday killed 14 newly reconciled fighters from pro-government and rebel ranks in an attack on a south Syrian village claimed by the militant Islamic State group.
Heavily outgunned, rebels in parts of Deraa province reached an agreement to surrender territory last week.
Rebels holed up in part of Daraa city are still in talks with Russian officers, with many of them aiming to secure safe passage to opposition-held areas of northern Syria, rebel officials said.
'The rebels are still inside Daraa city, ' Observatory head Rami Abdel Rahman said, but they had not yet handed over their heavy weapons and there were no signs of any evacuations.
Rebels are pinning hopes on the Russian military police to prevent the army from taking revenge and entering specific areas after complaints of widespread looting and some arrests in other towns in Daraa province they have gained control.