Heavy clashes rocked eastern districts of the Syrian capital on Sunday after opposition fighters launched a surprise assault on regime forces, a monitor and state television said.

Steady shelling and sniper fire could be heard across Damascus on Sunday as opposition factions launched an attack on regime positions in the city's east.

The clashes centered on a regime-held gap between two besieged opposition enclaves, the Jobar and Qaboun neighborhoods. The Ahrar al-Sham opposition group said fighters had "liberated" the area.

Opposition forces detonated two large car bombs at 5:20am on Sunday close to the Jobar neighborhood. Tahrir al-Sham claimed responsibility for the attack.

Opposition forces then advanced into the nearby Abbasiyn Square area, seizing several buildings and firing a barrage of rockets into multiple Damascus neighborhoods, according to Rami Abdelrahman of the UK-based Syrian Observatory for Human Rights.

Regime forces responded with nearly a dozen air strikes on Jobar, he added.

'The fight is still on'

Al Jazeera's Mohamed Al Jazaeri, reporting from near Damascus, said that at least 15 civilians had been killed after regime forces shelled residential neighborhoods in Eastern Ghouta, but that the fighting had since become less intense.

"This advance is the largest for opposition groups in over a year and a half," Al Jazaeri said. "Military operations have not stopped in the area but it has calmed down. There remains sniper shooting from both sides and regime forces are shelling Jobar neighborhood, as well as other areas controlled recently by the opposition."

Control of Jobar - which has been a battleground district for more than two years - is divided between opposition and allied fighters on one side, and regime forces on the other. It is one of three pockets in the Syrian capital still in opposition hands.

The recent fighting has resulted in opposition control of industrial areas in Al-Qaboun in addition to parts of Abbasiyn breaking a siege on the area and linking it to Jobar neighborhood, which is connected to Eastern Ghouta, Al Jazaeri said.

Joshua Landis, an expert on Syria at the University of Oklahoma, told Al Jazeera that the offensive had taken the regime by surprise and that its response was likely to be very significant.

"I don't think it's going to change the trajectory of the war, which has been seeing the regime make important gains and the opposition getting increasingly restricted. But it shows the opposition is far from dead. It shows also that this new combination led by [Tahrir al-Sham] is very potent," Landis said.

"The regime is going to realize that it cannot allow these two areas to linger there because they are beachheads for this Tahrir a-Sham group to make inroads into the Damascus area," he said, adding the regime would likely withdraw some forces from areas such as Homs and Hama to refocus on Damascus.
"It means that the fight is still on, there are many fronts to this war, and the opposition remains powerful."

Syrian regime state TV aired footage from Abbasiyn Square, typically buzzing with activity but now empty except for the sound of shelling.
Residents said artillery shells and rockets were landing in the heart of the city.

The Observatory said opposition shells hit several nearby districts in Damascus, including Bab Touma, Rukn al-Din and the Abbasiyin area.

Several schools announced they would close through Monday, and many civilians cowered inside in fear of stray bullets and shelling.

'From defensive to offensive'

According to the Observatory, the Faylaq al-Rahman group and the Fateh al-Sham Front were present in Jobar.

"This neighborhood is the most important front line because it's the closest opposition position to the heart of the capital," said Abdel Rahman.

Regime forces have long sought to push the opposition forces out of the district because of its proximity to the city centre in Damascus.

But with Sunday's attack, Abdel Rahman said, "opposition forces have shifted from a defensive position in Jobar to an offensive one".

"These are not intermittent clashes - these are ongoing attempts to advance," he said.

One opposition commander told the Associated Press news agency they launched the assault from Jobar as a way to relieve allied fighters in the nearby districts of Barzeh, Tishreen, and Qabun from regime attacks.

"This is to relieve the pressure on rebels with the regime not stopping its bombardment and artillery shelling," said Abu Abdo, a commander from Failaq al Rahman.

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.

Opposition and regime troops agreed to a nationwide cessation of hostilities in December, but fighting has continued across much of the country, including in the capital.

Opposition said the army had advanced in the last two days after weeks of bombardment and aerial strikes aimed at regaining control of strategic areas inside the capital, a few kms away from Bashar al Assad's seat of power.

The regime army had advanced towards a road between Qaboun and Barza, whose capture severed the links between the two besieged opposition districts where tens of thousands of people live.

"Taking this road would isolate Barza and Qaboun completely and with a security belt around it," said Abu Abdullah, another fighter with Failaq al Rahman opposition group.

The regime army and allied militias have been targeting the besieged Eastern Ghouta area, the biggest remaining opposition bastion around the capital, for months, making incremental gains.

It has undertaken a relentless bombing campaign of residential areas to force opposition to surrender and agree to deals that push them out of these areas.

PHOTO CAPTION

A road sign that shows the direction to Jobar district is pictured in the east of the capital Damascus, on March 19, 2017, Syria. REUTERS

Al-Jazeera