Syrian rebels seized most of a military airport in regime-controlled Sweida province Thursday and shot down a warplane nearby, a spokesman told AFP.
"The Southern Front has liberated Al-Thaala military airport and is carrying out mopping-up operations against remaining forces," the alliance's spokesman, Major Essam al-Rayes, told AFP.
The Syrian Observatory for Human rights also reported the rebel advance into the airport in the Druze-majority southern province.
"They have control of parts of the airport, which is used by the regime for aircraft that bomb Daraa and Damascus provinces," said Observatory director Rami Abdel Rahman.
But Syrian state television denied the claims, and interviewed the provincial governor, who accused media of spreading lies.
"There is no truth to claims that terrorist groups have occupied Al-Thaala in Sweida province," state television said, citing its reporter in the area.
"We're used to the criminal media and their falsehoods; the information being reported is baseless and life continues as normal in the province," Governor Atef al-Nadaf said.
Rayes also said Southern Front forces had shot down a warplane in the border region between Sweida and neighbouring Daraa province.
The Britain-based Observatory reported the same, and state television acknowledged that "a warplane went down in the southern region and an investigation into the causes is underway."
The Southern Front advance into Al-Thaala airport comes a day after the alliance, which groups moderate and Islamist rebel forces, seized the 52nd Brigade base in Daraa province.
Abdel Rahman said many of the regime forces who fled the 52nd Brigade as it was captured had withdrawn to Al-Thaala, which lies some 10 kilometres (six miles) away.
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Sweida province has been spared much of the fighting in Syria, and remains almost entirely under regime control.
Most of its residents are Druze, followers of a secretive offshoot of Shiite Islam, who made up around three percent of Syria's pre-war population of 23 million people.
The community has been somewhat divided during the country's uprising, with some members fighting alongside the government while others expressing sympathy for the opposition.
Mostly, the Druze have taken up arms only in defence of their areas, and have kept out of the fighting more broadly.
In a statement Thursday afternoon, the Southern Front sought to reassure Sweida's residents.
"We stress that the people of Sweida are our brothers and our people, and we... will not fight them," Rayes said in the statement.
"We are ready to confront hand-in-hand all threats to Sweida province if we are asked to do so."
The statement also condemned "in the strongest terms" the deaths of at least 20 Druze residents reportedly killed by Al-Qaeda affiliate Al-Nusra Front in Idlib on Wednesday.
The deaths in Qalb Lawzah sparked condemnation from Druze leaders in Syria and Lebanon.
The Southern Front has sought to distance itself from Al-Nusra and said in March it would not cooperate with the group.
But it has found itself fighting on the same side as the Al-Qaeda affiliate, including in battles against the jihadist Islamic State group.