Eastern Damascus was on Tuesday hit by its fiercest fighting in months between rebels and pro-regime forces, said the Syrian Observatory for Human Rights.
The air force pounded the rebel-held eastern neighbourhood of Jobar, as opposition fighters launched mortars into army-held parts of Damascus, wounding 18 people.
An AFP correspondent nearby said "very loud explosions could be heard starting late last night up until Tuesday afternoon."
Observatory director Rami Abdel Rahman said: "Starting dawn Tuesday, Jobar saw the fiercest fighting in months, coupled with intense aerial bombardment."
"Jobar is under army control, and the fighting is taking place on the neighbourhood's edges," he told AFP.
The air force carried out at least nine strikes on the neighbourhood, he said, adding rebels were fighting troops backed by pro-regime paramilitary forces.
Jobar, on the eastern edge of Damascus, is important because it is located at the entrance to the besieged, rebel-held Eastern Ghouta area on the outskirts of the capital.
It also neighbours Abbasiyeen, one Damascus' main squares where the army "deployed tanks... and shelled rebel areas of Jobar," Abdel Rahman told AFP.
Fighting in the area has intensified following a relative lull for months, after rebels launched an offensive and took an army checkpoint in Jobar.
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The army has since reclaimed the checkpoint.
Meanwhile, rebel fighters fired mortar rounds at regime-controlled areas of Damascus, wounding 18 people, state news agency SANA reported.
Mortar shells also hit the mixed Christian-Druze suburb of Jaramana, which is under army control, killing two civilians, said the Observatory.
The air force pounded the nearby rebel-held areas of Irbin and Hammuriyeh, killing a man and a child.
It meanwhile launched three air strikes on Mleiha, a rebel bastion in Eastern Ghouta that the army has been fighting to reclaim for months because of its strategic position near the Damascus airport road.
Forces loyal to President Bashar al-Assad, including Lebanon's Hezbollah, have waged a campaign for more than a year to crush rebel positions near Damascus.
Eastern Ghouta, a rebel rear base that the army has besieged for more than a year, was the scene of a massive chemical attack in August that killed hundreds.
In recent weeks, rebels in southern Damascus have also been fighting the jihadist Islamic State, after expelling it from four towns in Eastern Ghouta, according to the Observatory.
The Syrian conflict began as a peaceful movement for democratic change, but transformed into a civil war when Assad's regime unleashed a brutal crackdown on dissent.
The violence has killed more than 170,000 people and forced nearly half the population to flee their homes.