BEIRUT — 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 the attack today “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 morning.

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.

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 the 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.”

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 it would ask the United Nations to visit the site of the alleged attack.

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.