Former Prime Minister of France Laurent Fabius called for “reaction with force from the international community” if the allegation that chemical weapons were used in Syria. Backing the UN led investigation, Russia has called for Assad’s regime to cooperate with the probe and that rebel forces should guarantee safe passage for the team, according to Russian Foreign Ministry.

The UN Security Council said it was necessary to verify the alleged chemical weapons attack in Damascus suburb. Meanwhile, Russian Foreign Minister Sergei Lavrov and U.S. Secretary of State John Kerry had agreed that an objective investigation was needed into the allegation, according to Reuters.

US President Obama has said the alleged use of chemical weapons in Syria that killed hundreds, including children and women, is a “big event of grave concern.”

Although United States is still seeking for confirmation and Obama has ordered the US spy agencies to determine further information, the situation would “require America’s attention” if proved true.

"There's a great sense of urgency in the administration to gather information on the ground," State Department spokeswoman Jen Psaki said. "If these reports are true, it would be a flagrant use of chemical weapons by the regime. The president will consider his options and discuss it with his national security team."

Footages of alleged Syrian victims, including many children, revealed symptoms consistent to those caused by chemical poisoning or nerve gas. United Nations Secretary General Ban Ki Moon has called on the Syrian government to allow a U.N. inspection team currently in Syria to examine previous claims of chemical weapons use swiftly to swiftly access the site of the latest alleged attack.

Wednesday’s attack came in the middle of the night, although it did not come as a surprise. Reports of fierce clashes between Free Syrian Army rebels and government forces were posted by pro-opposition Local Coordination Committees, according to BBC. The locations of the attacks are at the rebel strongholds in the Ghouta agricultural belt east of Damascus – towns of Irbin, Jobar, Zamzlka and Ain Tarma. And to the west of Damascus, the town Muadhamiya is named.

Ban said on Friday in South Korea that any use of chemical weapons in Syria would constitute a “crime against humanity” and that there was “no time to lose” in pinpointing the perpetrators of the alleged attack which the opposition says killed hundreds, according to AFP.

The images of victims from this incident, including many children, are “heartbreaking and sickening,” Ban said.

A citizen journalism image provided by the Local Committee of Arbeen which has been authenticated based on contents and AP reporting, shows Syrian citizens trying to identify dead bodies, after an alleged poison gas attack by government forces.

A boy, affected by what activists say was a gas attack, is treated at a medical center in the Damascus suburbs of Saqba. (Reuters)

“Any use of chemical weapons anywhere, by anybody, under any circumstances, would violate international law,” he said. “Such a crime against humanity should result in serious consequences for the perpetrator.”

Ban had instructed U.N. High Representative for Disarmament Affairs, Angela Kane, to immediately travel to Damascus to press the case for an urgent investigation.

“I can think of no good reason why any party, either government or opposition forces, would decline this opportunity to get to the truth of the matter,” he said.

Assad’s government has denied using chemical weapons, particularly at a time when the UN was in Syria to inspect three sites where other such attacks allegedly took place. It would be “political suicide” to do so, said a senior security source, the AFP reports.

Former US Army Chemical Corps officer Dan Kaszeta told AFP, “It would be relatively hard to fake” the amount of video footage that has surfaced.

“There’s a lot of stuff that goes on in that video and a lot of victims sadly are children, and it’s hard to get small children to consistently fake things,” he said.

The Syrian Observatory for Human Rights, which has a network of activists and medics on the ground, said air strikes and bombardments had been launched across Damascus province while the fighting raged in the southwest of the capital.

Experts said convulsions, pinpoint pupils and labored breathing seen in footage of alleged victims ‘likely’ to be symptoms of nerve gas, but they also insisted only blood and urine samples gathered from victims could provide definite proof.

“I was skeptical about the claims of nerve agent neurotoxicants (but) I have revised my position on that a bit on the basis of footage I have seen… where a number of symptoms consistent with organophosphorus poisoning” were apparent, said chemical weapons specialist Jean Pascal Zanders, the AFP reports.

Organophosphorus is a chemical compound used in nerve agents like sarin and kills by asphyxiation.

Ban said the death toll has now surged past 100,000 people in Syria’s 29-month war, and the war continues to worsen. Meanwhile, two U.N. agencies said Friday that the number of child refugees from Syria has now passed a landmark threshold, with 1 million forced to flee during the conflict, according to CNN.

About 740,000 of the children registered are aged under 11, U.N. children’s agency UNICEF said. Most of them are staying in Lebanon, Jordan, Turkey, Iraq and Egypt.

“This one millionth child refugee is not just another number,” said UNICEF Executive Director Anthony Lake. “This is a real child ripped from home, may be even from a family, facing horrors we can only begin to comprehend.”

Inside Syria, at least 7,000 children have been killed during the conflict and another 2 million children have been internally displaced, according to the Office of the High Commissioner for Human Rights. Wednesday’s alleged attack added to the number of children killed in the country’s conflict.