BEIRUT (AP) — Syrian regime forces fired intense artillery and rocket barrages today on the eastern suburbs of Damascus amid a fierce government offensive in what two pro-opposition groups claimed was a “poisonous gas” attack that killed at least 100 people, including many children.

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 today’s attack “absolutely baseless” — would employ chemical agents at this time.

France’s president demanded the United Nations be granted access to the site of today’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 today 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 today, 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 not clear whether the victims died from shelling or toxic gas.