The government has denied allegations it used chemical weapons in artillery barrages on the area known as eastern Ghouta on Wednesday as "absolutely baseless."
The United States, Britain and France have demanded that a team of U.N. experts already in Syria be granted immediate access to investigate the site.
Syrian opposition figures and activists have reported widely varying death tolls from Wednesday's attack, from 136 to as high as 1,300. But even the most conservative tally would make it the deadliest alleged chemical attack in Syria's civil war.
The Britain-based Syrian Observatory for Human Rights said it had no word on casualties in the Thursday morning bombing of eastern Ghouta. It said Syrian warplanes conducted several air raids on eastern and western suburbs of Damascus, including three that took place within five minutes.
The Local Coordination Committees, another activist group, said President Bashar Assad's forces were bombing eastern Ghouta from the Qasioun mountain overlooking Damascus. It also reported several air raids on the suburbs.
Wednesday's alleged chemical attack had killed scores of children. The small, lifeless bodies appeared in amateur videos, wrapped in white cloths, their pale skin unmarked by any wounds.
Images of dead children lined shoulder to shoulder in rooms and of others being treated for breathing problems brought worldwide condemnation and shock.
Mohammed Abdullah, an activist in the suburb of Saqba told The Associated Press via Skype on Thursday that most of the dead were buried hours after the attack in collective graves in different areas in eastern Ghouta. The burials took place quickly for fear the bodies might decompose as a result of the heat and lack of electricity, he said.
Relatives identified some of their dead family members before burial while unidentified victims were photographed and their graves tagged with a number in case their loved ones come to collect their bodies in the future.
"Most of the dead were buried in mass graves," Abdullah said.
UNICEF said in a statement that the reports of attacks on civilians, presumably including children, were "deeply disturbing."
"Such horrific acts should be a reminder to all the parties and all who have influence on them that this terrible conflict has gone on far too long and children have suffered more than enough," UNICEF said. "Children must be protected, and those who fail to protect them will be held accountable."
From New York, the U.N. Security Council called for "a thorough, impartial and prompt investigation" of the latest allegation of chemical weapons' use in Syria.
Syria's state media quoted on Thursday an unnamed Foreign Ministry official, according to its standard practice, as saying that allowing the U.N. team to go to Ghouta would require an agreement between the Syrian government and the United Nations.
A 20-member U.N. team led by Swedish chemical weapons expert Ake Sellstrom is in Damascus since Sunday to investigate three sites where chemical weapons attacks allegedly occurred in the past: the village of Khan al-Assal just west of the embattled northern city of Aleppo and two other locations being kept secret for security reasons.
France, meanwhile, raised the possibility of the use of force in Syria if it is proven that Assad's regime used chemical weapons, while Turkey said several red lines have been crossed.
"We need a reaction by the international community .... a reaction of force," said French Foreign Minister Laurent Fabius. He excluded boots on the ground as an option, though, and declined to be "more precise" on the type of force that could be used.
Yuval Steinitz, Israel's minister for intelligence and strategic affairs, said their "intelligence estimates" concluded that chemical weapons indeed were used, and appeared to blame Assad, calling his regime "exceptionally cruel."
In Germany, Turkish and German foreign ministers underlined demands for the Syrian regime to allow U.N. inspectors to investigate the claims. The Turkish diplomat called for new sanctions.
"Several red lines have been crossed - if sanctions are not imposed immediately, then we will lose our power to deter," said Turkish Foreign Minister Ahmet Davutoglu.
He added that he had spoken to U.N. chief Ban Ki-moon and told him that "the U.N. must not behave hesitantly anymore, sanctions must now be imposed."
German Foreign Minister Guido Westerwelle said the Syrian opposition's allegations were "so serious, so monstrous that it is necessary to enable a real examination before talking or speculating about consequences."
The unrest in Syria began in March 2011 and later exploded into a civil war. More than 100,000 people have been killed in the conflict so far, according to U.N. figures.