Air strikes hit four rebel-held areas of the embattled Syrian city of Aleppo and a southern village on Sunday, which are the first raids since a ceasefire was announced by the US and Russia last week.
The Britain based Syrian Observatory for Human Rights said that one woman was killed and many others were injured but it was not clear who conducted the air raids.
The monitor also said that 10 people, including a child were killed when two barrel bombs hit the opposition held, southern province of Deraa. The head of the Observatory, Rami Abdel Rahman told Al Jazeera, "Today was the highest death toll since the truce began."
Moscow put the blame for Sunday's violence on the opposition. Russian Defence Ministry's spokesperson Major General Igor Konashenkov, said in an emailed statement to the Associated Press news agency that "opposition and terrorists" are using the ceasefire to "boost their forces and prepare for renewed hostilities."
The seven-day ceasefire was supposed to end on Sunday midnight. The renewed air strikes come just after US-led coalition on Saturday, 17 September, in an air strike killed at least 62 Syrian soldiers, which led to a war of words between Moscow and Washington.
Russia said that the future of the ceasefire is in doubt after the raids struck Syrian soldiers. The US military has said that it may have mistakenly hit Syrian forces while conducting strikes against Islamic State (Isis) in eastern Syria. The ceasefire had largely held but violations continued to persist and aid convoys could not reach the besieged areas of Aleppo.
However, in an interview to BBC World TV, Assad's media adviser, Bouthaina Shaaban, said: "The United States, the superpower, the greatest country in the world, makes mistakes in targeting the army? I mean, this doesn't make sense to ask. The other explanation is that there is one authority in the United States who wanted to conduct this, the other doesn't want to. And that's why they are finding it very difficult to implement what they agreed upon with the Russian."
On Sunday, Syrian state media reported that scores of residents of Aleppo had left the rebel-held areas and were taken to shelters in the government-held areas. Aleppo's governor Hussein Diab, asked the insurgents in the eastern neighbourhoods to surrender themselves and take advantage of an Amnesty deal recently announced by Bashar al-Assad.
"We are at a new stage that requires making the decision to embrace reconciliation," Diab added in a statement carried by Sanaa news agency.