Accelerating bombardment by the government and its allies killed at least 35 people in the rebel-held eastern Ghouta region near Damascus in 24 hours, a war monitor said on Monday.
The death toll from air strikes, rocket fire and shelling on several areas of the besieged enclave of towns and farms included five children, the Britain-based Syrian Observatory for Human Rights said.
Rebel groups in eastern Ghouta fired mortars at areas of Damascus held by the government, killing a child and injuring eight other people, Syrian state media said.
Eastern Ghouta, the largest rebel bastion left near the capital, is home to almost 400,000 people according to the United Nations and has been besieged since 2013.
Syrian President Bashar al-Assad has gained momentum in the war since Russia entered on his side in 2015, pushing the rebels from big cities and retaking much of central and eastern Syria from Islamic State.
The Observatory said the army and its allies were preparing a military offensive in eastern Ghouta.
Jihadist rebels, including some loyal to Islamic State, also hold much of the Yarmouk Palestinian refugee camp in the southern suburbs of Damascus.
