Civilian deaths as a result of air strikes on an agreed "de-escalation zone" are threatening a Russian-backed truce. The rebel-held town that was struck has been the focus of government attacks.
Air strikes have killed at least nine people in the town near Damascus, while shelling from the rebel-held area landed near the Russian embassy, a war monitor reports.
The Syrian Observatory for Human Rights said the deaths in the air strikes overnight on Monday (local time) in the Eastern Ghouta town of Arbin marked the first civilian casualties since a Russian-backed truce in the area came into effect. The Syrian military declared a cessation of hostilities there on Saturday.
But Russia, a military ally of President Bashar al-Assad, dismissed reports of air strikes in the area as "an absolute lie" meant to discredit Moscow's peacemaking efforts.
"During working contacts with representatives of opposition groups in Eastern Ghouta it was confirmed that no military actions had been conducted in this de-escalation zone, there had been no air strikes," the Russian defence ministry spokesman said in a statement on Tuesday.
Russia said on Monday it had deployed military police in Eastern Ghouta to try to enforce a de-escalation zone it said it had agreed with the Syrian opposition there.
In a second statement, issued late on Tuesday, the Russian Defence Ministry said it had delivered 10 tons of food and medical supplies to Eastern Ghouta, and evacuated sick and injured civilians from opposition-held areas.
Tuesday's shelling near the Russian embassy marked the first time rebels had hit government-held areas of central Damascus since the truce began.
The Observatory said the overnight air strikes wounded 30 people in Eastern Ghouta while another four were injured by further air strikes that targeted the area on Tuesday morning.
The Civil Defence for rural Damascus, a rescue service operating in the area, said the dead included five children and two women.
In a statement on its Facebook page, it put the number of wounded and missing at 50. The air strikes hit the area at 11pm on Tuesday.
There was no immediate comment from the Syrian military on the report and no mention of air strikes by state media.