At least 10 people have been killed by air strikes in the opposition-held Damascus suburb of Ein Tarma, according to a UK-based monitor.
The Syrian Observatory for Human Rights (SOHR) said at least two children were among those killed in the air strikes on Friday.
The assault took place in the Eastern Ghouta region, which has been partially besieged by the Syrian government since 2013.
Located about 15km outside of Damascus, the region is the biggest remaining oppisition bastion in the Syrian capital's suburbs.
SOHR said several people were seriously injured and the death toll was expected to rise.
In recent weeks, government forces have been heavily bombarding Ein Terma, which links the Eastern Ghouta area to the opposition-held Damascus neighbourhood of Jobar, according to SOHR.
Video posted by the Syria Civil Defence - also known as The White Helmets - shows what is believed to be the aftermath of Friday's attack.
One video uploaded by the group shows a child being rescued from the rubble of a destroyed building.
The videos cannot be independently verified.
According to SOHR, Friday's air strike is the biggest loss of life in the Eastern Ghouta region since April when 18 people were killed in an attack on Saqba.
In 2013, the Syrian government banned civilians from going into or out of the enclave, allowing only some food deliveries.
Eastern Ghouta is made up of 22 communities and has seen Russian and Syrian air attacks on markets, schools, and hospitals in many of them.
The area is part of an agreement, signed in May by Russia, Turkey and Iran, to set up four so-called de-escalation zones in Syria.
The deal called for the cessation of hostilities between armed groups and forces fighting on behalf of President Bashar al-Assad's government.
But disagreements over its details have delayed its implementation.
A separate ceasefire, brokered by the US, Russia and Jordan earlier this month, in Syria's southwest appears to be holding, according to SOHR.
More than 470,000 people have been killed in Syria since the conflict began in March 2011.
