Downing of warplane comes day after government launched attack in southern province of Sweida
US-backed rebel groups shot down a Syrian government warplane on Tuesday near a ceasefire zone in the country's south, the factions and a monitoring group said.
Two rebel groups that operate in southeast Syria, the Lions of the East Army and the Ahmad al-Abdo Forces, issued a joint statement on Tuesday saying they had downed the aircraft.
"The plane was shot down and crashed in government-controlled territory. We have no information on the pilot," said Fares al-Munjed, communications head for the Ahmad al-Abdo Forces.
The two groups are part of the Southern Front of the Free Syrian Army, which is heavily supported by neighbouring Jordan and the US.
The Syrian Observatory for Human Rights monitor confirmed that the rebel groups had hit the plane near a village on the administrative border between the provinces of rural Damascus and Sweida.
Sweida province is part of a new ceasefire deal negotiated by the United States, Russia, and Jordan that went into effect on Sunday.
The deal has brought relative quiet to most of the provinces covered - Daraa, Quneitra and Sweida - though outbreaks of violence have been reported.
In Sweida, government forces launched an attack on Monday on the Ahmad al-Abdo Forces and the Lions of the East Army.
The monitor said the government had captured a string of hilltops and villages in the area.
But Syrian state media named those same positions as territory that government forces had captured from the Islamic State (IS) group.
"Our forces and allies captured several areas, villages, hilltops and commanding positions in the eastern countryside of Sweida after eliminating large numbers of IS terrorists," the state news agency SANA said.
Fighting continued into Tuesday over a series of hilltops and villages in the province, the monitor and rebels said.
Calls for expanded ceasefire
The clashes come amid calls by Iran to expand the ceasefire.
"The [ceasefire] agreement can be fruitful if it is expanded to all of Syria and includes all of the area that we discussed in the Astana talks for de-escalating the tension," Iranian foreign ministry spokesman Bahram Qasemi was quoted as saying by the Tasnim news agency.
"Iran is seeking Syria's sovereignty and security so a ceasefire cannot be limited to a certain location. No agreement would be successful without taking the realities on the ground into account," he added.
The United States, Russia and Jordan announced a ceasefire and "de-escalation agreement" for southwestern Syria on Friday after a meeting between the US and Russian presidents at the G20 summit in Hamburg.
So far, the deal announced on Friday has brought quiet to most of the three provinces covered: Daraa, Quneitra and Sweida.
But in addition to the Sweida clashes, there have been other limited violations according to the monitor, including government shelling and exchanges of fire with rebels in Daraa.
In Quneitra province, there were also reports of sporadic machine gun fire from both sides, though there were no casualties in any of the incidents, the monitor said.
Sunday's ceasefire went into effect just before new peace talks in Geneva.
More than 320,000 people have been killed in Syria since the conflict began in March 2011 with anti-government protests.