A coalition of rebel groups have launched a follow-up assault to June’s "Southern Storm" offensive to take the strategic regime-held city of Daraa in the south of Syria.
Rebels including al-Qaeda's Syrian franchise on Thursday launched a fresh offensive on the major southern city of Daraa, saying their aim was to "purify" the area.
"Operation Storm of Truth" was announced on Twitter by the Southern Front, an alliance of rebel groups, "to purify the province of Daraa from the filth of the gangs of President Bashar al-Assad".
"The violent attack began this morning on regime-held parts of Daraa city, with both sides exchanging shellfire," said Rami Abdel Rahman, director of the UK-based Syrian Observatory for Human Rights.
Opposition groups already control parts of the city and about 70 percent of the province of the same name, which borders Jordan
"The groups are attacking government positions in northern parts of the city, but they haven't seized buildings yet," Rahman added.
The 'cradle of the revolution' Al-Qaeda affiliate, the Nusra Front, and other Islamist militias are taking part in the fighting in Daraa, dubbed the "cradle of the revolution" against Assad which began in 2011, triggering Syria's civil war.
An important rebel military commander has died in the assault, said the opposition-leaning Observatory, which relies on a vast network of sources within the country.
Abou Hadi Abboud, who headed the Fallujah al-Houran opposition group, part of the Southern Front military coalition, was killed on Thursday when a shell hit his car in Daraa province.
"He is the most important rebel commander to be killed since the beginning of the Daraa offensive in June," Abdel Rahman said.
Regime aircraft have conducted at least 21 air raids and dropped 32 barrel bombs on rebel positions.
Late on Thursday, a barrel bomb attack on the West Ghariya area of Daraa province killed 13 civilians, including two children.
"The two children were just reduced to body parts. From the waist down, there's nothing," Abdel Rahman said.
Another three children and a woman were killed in a rocket attack on a rebel-held neighbourhood in Daraa city.
Opposition groups already control parts of the city and about 70 percent of the province of the same name, which borders Jordan.
Thursday's offensive appears to be a continuation of an assault in June, launched by the same groups but dubbed "Southern Storm". That round of fighting left at least 60 rebels, 18 loyalists and 11 civilians dead.
The Syrian regime has already lost two provincial capitals - Idlib in the northwest, which is held by a rebel alliance including Nusra, and Raqqa in the Euphrates valley, held by the Islamic State group.
In a separate development on Thursday, intense clashes between troops and IS fighters in Aleppo province in the north left at least 12 government forces and one extremist fighter dead.
The government fighters were able to retake a strategic hilltop northeast of Aleppo city, the Observatory said.
At least 230,000 people have been killed since the Syrian conflict began.