The toll in Syrian government air strikes on a rebel-held town outside Damascus neared 100 Monday, as the UN's humanitarian chief expressed horror and appealed for civilians to be protected.
Sunday's series of raids on the town of Douma, in the rebel bastion of Eastern Ghouta, was one of the bloodiest regime attacks in Syria's four-year war.
They came almost exactly two years after devastating chemical weapons attacks on the same region that much of the international community blamed on the Syrian government.
The National Coalition, Syria's main opposition body in exile, condemned both the air strikes and the "lukewarm response" by the international community towards the war's civilian casualties.
At least 96 people were killed in the 10 air strikes on a marketplace, according to the Syrian Observatory for Human Rights, a Britain-based monitor.
Another 240 people were wounded, and the death toll continues to rise as those in a serious condition succumb to their injuries.
Observatory head Rami Abdel Rahman said government aircraft carried out another four air strikes on Douma on Monday morning, but he had no immediate details on casualties.
An AFP photographer on Sunday described the attack as the worst he had covered in the town.
He saw dozens of bodies lined up on the bloodied floors of one of Douma's makeshift clinics, as medics struggled to treat waves of wounded.
Two young boys with bloodied faces sat on a stretcher as they awaited treatment, one resting as though exhausted while the other cried.
On Monday, the photographer said residents were burying the victims of the attack.
"They went early to the cemetery to begin the burials," he said.
"After each massacre, they bury the dead one on top of each other. Gravediggers have had to create a mass grave that is four layers deep to accommodate the dead."
Eastern Ghouta, a rebel bastion regularly targeted by government air strikes, has been under a suffocating siege for nearly two years.
Amnesty International last week accused the government of committing war crimes there, saying its heavy aerial bombardment of the area was compounding the misery created by the blockade.
On Monday, the UN's humanitarian chief Stephen O'Brien, on his first trip to Syria since taking the post in May, fiercely condemned attacks on civilians.
At a news conference in Damascus, he said he was "horrified by the total disrespect for civilian life in this conflict".
"I am particularly appalled by reports of air strikes yesterday causing scores of civilian deaths and hundreds injured right in the centre of Douma, a besieged area of Damascus," O'Brien said.
"I appeal to each and every party to this protracted conflict to protect civilians and respect international humanitarian law."
During his three-day visit, O'Brien met officials including Foreign Minister Walid Muallem to discuss ways of improving UN humanitarian operations in the country.
But the top aid chief said he remained "concerned" about the fate of around 4.6 million Syrians living in besieged or hard-to-reach areas.
The Observatory's Abdel Rahman described Sunday's Douma attacks as part of the regime's "scorched earth policy".
"The regime wants to show that it can kill as many people as it wants, without caring about the international community," he said.
Abdel Rahman said Douma is the largest and most important rebel stronghold in Damascus province.
At least 240,000 people have been killed in Syria's war, which began in March 2011 with protests against President Bashar al-Assad's regime.
In an emailed statement, the opposition National Coalition accused the government of "deliberately" targeting civilians in Douma.
"The air strikes were deliberate in that Assad's jet fighters fired missiles on marketplaces at (a) busy time when they are densely crowded with the intention of inflicting as many civilian casualties as possible," the statement read.
But it also said the international community's failure to respond to such atrocities contributed to the violence.
"The UN Security Council and the international community's lukewarm response is a contributing factor in the escalation of massacres against Syrian civilians," the Coalition said.
It criticised international bodies, including the Security Council, for failing to condemn the massacres or do more to protect civilians in Syria.