DAMASCUS - A car bomb outside a mosque near Damascus killed at least 40 people on Friday, an NGO said, as a top UN official expressed mounting concern over hundreds of thousands of trapped civilians.
Dozens of people were wounded in the car bombing in the town of Suq Wadi Barada, said the Britain-based Syrian Observatory for Human Rights, which relies on a network of activists and other witnesses.
The Syrian government and opposition exchanged blame for the carnage. Suq Wadi Barada is under rebel control and ringed by troops loyal to the regime of President Bashar al-Assad.
"The toll from a car bomb explosion that detonated after Friday prayers in Suq Wadi Barada has risen to 40, including seven children and a woman," said the Observatory.
"The number of dead is likely to rise because there are dozens of wounded, most of them in critical condition," it added.
State news agency SANA had earlier reported the blast, blaming "terrorists", the term the Assad regime uses for forces fighting to oust it.
SANA said "the car exploded while the terrorists were packing it with explosives".
The opposition National Coalition meanwhile blamed the Assad regime for the "massacre" caused by what it said were two car bombs placed outside the Osama Bin Zeid mosque in Suq Wadi Barada.
"Bashar al-Assad's gangs detonated two car bombs at midday... that were planted in front of the Osama Bin Zeid mosque in Suq Wadi Barada," the Coalition said in a statement.
"The regime's constant commission of massacres makes it the duty of countries of the free world, the friends of the Syrian people, as well as international human rights and humanitarian organisations to fulfil their responsibilities towards civilians," it added.
They must "protect the lives of Syrians and uphold their rights".
Car bombings have plagued Syria in recent months, killing scores across the country.
Syrian state TV meanwhile reported that Abu Mohammed al-Jawlani, leader of the Al-Nusra Front, a powerful jihadist rebel group linked to Al-Qaeda, was killed in northwestern Latakia province, but the Front later said he was in good health.
In other violence an army ambush east of Damascus killed some 24 rebels, the Observatory said, as SANA put the toll at 40.
The outskirts of the capital have seen fierce fighting in recent days as Assad's troops try to tighten the noose around rebel areas.
The army has closed in on Eastern Ghouta, a ring of suburbs besieged for months, which was targeted in an August chemical attack that killed hundreds of people and almost led to punitive US strikes.
UN and US officials have expressed concern about Eastern Ghouta and other besieged Damascus suburbs, following reports of severe food shortages and rising malnutrition.