Mortar rounds fired from the rebel-held Eastern Ghouta region onto residential areas of Damascus left eight civilians dead and 23 wounded, the official SANA news agency reported.
The attack came after the regime fired rockets onto the Eastern Ghouta town of Douma earlier in the day, killing five civilians, according to the Syrian Observatory for Human Rights, a British-based monitor.
Eastern Ghouta, which is largely controlled by the Jaish al-Islam (Army of Islam) rebel group, is regularly bombarded by government forces.
The monitor also gave the same toll as state media for the attack on Damascus and said some of the wounded there were in critical condition.
More than 260,000 people have been killed since Syria's conflict erupted in 2011 with protests against President Bashar al-Assad's government.