The alliance, also involving powerful Islamist group Ahrar al-Sham, bombarded loyalist positions with mortar and artillery fire, the Syrian Observatory for Human Rights said.
Syria's official SANA news agency said "terrorists hit neighbourhoods of Daraa city with mortar rounds and gas canister bombs," adding that there were reports of casualties.
"Army units foiled attempts by terrorist groups to attack several military positions in Daraa province destroying several armoured vehicles and killing dozens of terrorists," state television said.
Around 70 per cent of Daraa province is under the control of rebel groups, who have made several advances in the region in recent weeks.
In early June, rebels from the Southern Front coalition seized the 52nd Brigade base and advanced to the border between Daraa and Sweida, a mainly Druze province to the east which is largely regime-controlled.