A 20-member U.N. chemical weapons team is currently in Syria to investigate three sites where chemical weapons attacks allegedly occurred over the past year. Their presence raises questions about why the regime - which called the claims of the attack Wednesday "absolutely baseless" - would employ chemical agents at this time.
France's president demanded the United Nations be granted access to the site of Wednesday's alleged attack, while Britain's foreign secretary said if the claims are verified it would mark "a shocking escalation of the use of chemical weapons in Syria."
The heavy shelling early Wednesday pounded the capital's eastern suburbs of Zamalka, Arbeen and Ein Tarma, according to the Britain-based Syrian Observatory for Human Rights monitoring group. The intensive bombardment as well as the sound of fighter jets could be heard by residents of the Syrian capital throughout the night and early Wednesday, and gray smoke hung over towns in the eastern suburbs.
Observatory director Rami Abdul-Rahman said the activists in the area said "poisonous gas" was fired in rockets as well as from the air in the attack. He added that he has documented at least 100 deaths, but said it was no clear whether the victims died from shelling or toxic gas.
Another group, the Local Coordination Committees, said hundreds of people were killed or injured in the shelling. Such different figures from activists groups are common in the immediate aftermaths of attacks in Syria, where the government restricts foreign and domestic reporting.
The Syrian government denied the reports of Wednesday's chemical weapons attack.
"They are an attempt to divert the U.N. commission on chemical weapons from carrying out its mission," the state-run SANA news agency said, quoting an unnamed government official, as is its standard practice.
The head of the U.N. team in Syria to investigate previous claims of alleged chemical attacks said he wants to look into the latest claims.
Speaking to Swedish broadcaster SVT, Ake Sellstrom said the high numbers of killed and wounded being reported "sound suspicious."
"It looks like something we need to look into," Sellstrom, who is Swedish, was quoted as saying.
He said a formal request from a member state would have to go through the U.N. channels and Syria would need to agree - and there is no guarantee that it would.
France said they will ask the United Nations to visit the site of Wednesday's alleged attack.
President Francois Hollande, speaking at a regular Cabinet meeting, said the latest allegations "require verification and confirmation," according to government spokeswoman Najat Vallaud-Belkacem.
Hollande would ask the U.N. to go to the site "to shed full light" on the allegations.
The Syrian government has long denied claims by the opposition on chemical weapons use, saying rebels fighting to overthrow President Bashar Assad's government have used such weapons.
Following Wednesday's reports, the Observatory called upon the U.N. team in Syria and all international organizations "to visit the stricken areas and to guarantee that medical and relief supplies reach the people as soon as possible." It also called for an investigation into the attack.
Mohammed Saeed, an activist in the area, told The Associated Press via Skype that hundreds of dead and injured people were rushed to six makeshift hospitals in the eastern suburbs of Damascus.
"This is a massacre by chemical weapons," said Saeed. "The visit by the U.N. team is a joke ... Bashar is using the weapons and telling the world that he does not care."
An activist group in the town of Arbeen east of Damascus posted on its Facebook page pictures purporting to show rows of Syrian children, wrapped in white death shrouds, and others, with chests bared. There appeared to be very little signs of blood or physical wounds on the bodies.
An amateur video showed four children on the floor of a makeshift hospital, appearing to be unconscious as a doctor is seen giving them some sort of shots. A bit later, a child starts shaking slowly.
"Is this baby girl a terrorist," a man could be heard saying. "God willing, we will bring his regime down. He (Assad) is killing Sunni children in front of the whole world."
"Oh, Bashar, you son of a dog," says another man. "We will come and get you in your place."
Another video shows bodies of children lined on the floor of a room, showing no signs of life.
The photos and videos distributed by activists to support their claims were consistent with AP reporting of shelling in the area, though it was not known if the victims died from a poisonous gas attack.
Sellstrom's team of U.N. experts is meant to probe three sites: the village of Khan al-Assal just west of the embattled northern city of Aleppo and two other locations, which are being kept secret for security reasons.
Wednesday's claim of the chemical attack, if confirmed, would be the most serious since the March 19 incident in Khan al-Assal when at least 30 people were killed. Assad's regime and the rebels have blamed each other for that attack.
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.