Heavy clashes rocked eastern districts of the Syrian capital on Sunday as rebels and jihadists tried to fight their way into the city centre in a surprise assault on government forces.
Steady shelling and sniper fire could be heard across Damascus on Sunday as rebel factions allied with former Al-Qaeda affiliate Fateh al-Sham Front launched an attack on regime positions in the city's east.
The attack began early Sunday "with two car bombs and several suicide attackers" on the Jobar district, said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights monitoring group.
Rebels then advanced into the nearby Abbasid Square area, seizing several buildings and firing a barrage of rockets into multiple Damascus neighbourhoods, Abdel Rahman said.
Government forces responded with nearly a dozen air strikes on Jobar, he added.
Syrian state television reported that the army was "thwarting an attack by terrorists" with artillery fire and had ordered residents to stay inside.
It aired footage from Abbasid Square, typically buzzing with activity but now empty except for the sound of shelling.
AFP correspondents in Damascus said army units had sealed off the routes into the square, where a thick column of smoke was rising into the cloudy sky.
Several schools announced they would close through Monday, and many civilians cowered inside in fear of stray bullets and shelling.
The attack on Damascus comes just days before a fresh round of UN-brokered peace talks in Geneva aiming to put an end to Syria's six-year war.
Rebels and government troops agreed to a nationwide cessation of hostilities in December, but fighting has continued across much of the country, including in the capital.
Rebels have shifted from defensive to offensive: Observatory
Control of Jobar -- which has been a battleground for more than two years -- is divided between rebels and allied jihadists and government forces.
According to the Observatory, the Islamist Faylaq al-Rahman rebel group and the Fateh al-Sham Front -- known as Al-Nusra Front before it broke ties with Al-Qaeda -- are present in Jobar.
Government forces have long sought to push the rebels out of the district because of its proximity to the city centre in Damascus.
But with Sunday's attack, Abdel Rahman said, "rebels have shifted from a defensive position in Jobar into an offensive one".
"These are not intermittent clashes -- these are ongoing attempts to advance," he said.
The Observatory said rebels had launched the attack as a way to relieve allied fighters in the nearby districts of Barzeh, Tishreen and Qabun from government attacks.
"Nine regime forces and at least 12 Islamist rebels were killed" in those districts over the last 24 hours, the Observatory said.
More than 320,000 people have been killed since Syria's conflict erupted six years ago with protests against Assad's rule.
After a government crackdown, the uprising turned into an all-out war that has drawn in world powers on nearly all sides.
On Sunday, Israeli Defence Minister Avigdor Lieberman threatened to destroy Syria's air defence systems after they fired ground-to-air missiles at Israeli warplanes on Friday.
Syria's army said it shot down an Israeli jet and hit another as they were carrying out early morning strikes near the famed desert city of Palmyra.
Israel denied any planes were hit and said it was targeting weapons bound for Lebanon's Hezbollah movement, which is backing Assad in Syria.
The United Nations has sponsored peace talks to end the conflict since 2012, to no avail.
Government representatives and opposition figures are set to meet for a fourth round of negotiations on March 23 in Switzerland.