More than 30 people have been killed in the most lethal rebel bombardment of the city of Aleppo since Syria's conflict started four years ago, a group monitoring the war said on Tuesday.
The United Nations special envoy for Syria, Staffan de Mistura, condemned the shelling and called it an indiscriminate attack on civilians.
While large civilian death tolls are frequently reported as a result of Syrian army aerial bombardment of rebel-held parts of the northwestern city, lethal shelling of government-controlled areas is more unusual.
Analysts expect intensified battles for Aleppo and other parts of western Syria this summer after insurgent advances in the northwest, central Syria and the south.
The British-based Syrian Observatory for Human Rights said
34 people were killed, including 12 children, and about 190 were wounded in the bombardment by rebels who are seeking control of the divided city.
State media had said on Monday that at least 23 people were killed. The attack targeted a mosque where children were taking religious lessons as well as other neighbourhoods, it said.
State news agency SANA published a picture of a limp, blood-soaked child in the arms of a man and another of an older woman in white clothes stained in blood and being attended to by medics.
The Observatory said the insurgents fired more than 300 shells on government-held neighbourhoods in Aleppo.
The Syrian army and rebels have been in a long battle for Aleppo, which was the country's economic and industrial hub
before rebels took over parts of the city in July 2012.
Seizing it would be a big victory for the insurgents against stretched government forces, which have been forced back in other parts of Syria. The conflict has killed more than 220,000 people and driven millions from their homes since 2011.
The office of UN envoy de Mistura, who is visiting Damascus to meet government officials, condemned the rebel shelling.
"This indiscriminate attack on civilians in the city of Aleppo took place at the very time when Mr. de Mistura was in Damascus raising with the government the issue of the protection of civilians and the urgent need to stop the use of barrel bombs."
The government should not retaliate against populated areas by using barrel bombs, it said.
"The Syrian government…is expected like any government to refrain from killing its own civilians," it said.
Syrian President Bashar al-Assad has said the military does not use barrel bombs.
De Mistura has previously tried to broker a ceasefire in Aleppo, which has been carved up between government forces and various insurgent groups.
Insurgents targeting the capital Damascus further south fired at least 10 rocket-propelled grenades on Tuesday which fell in areas near the Russian Embassy, the Observatory said. It gave no details on casualties.
