DAMASCUS - Two Syrian pro-opposition groups are claiming that government forces carried out a "poisonous gas” attack near the capital Damascus, leaving dozens of people dead, the Associated Press news agency has reported.

The two groups quote activists as saying that regime forces fired "rockets with poisonous gas heads” in the alleged attack early on Wednesday.

The Britain-based Syrian Observatory for Human Rights says the shelling was intense and hit the eastern suburbs of Zamalka, Arbeen and Ein Tarma.

It says at least 100 were killed, while the Local Coordination Committees said hundreds of people were killed or injured in the shelling.

Main opposition group, Syrian National Coalition, accused the regime of killing more than 650 people in the attack.

"Over 650 confirmed dead result of deadly chemical weapon attack in Syria,” the National Coalition said on Twitter. The Syrian authorities denied charges that the army used chemical arms, saying the reports were intended to hinder the mission of UN inspectors now in the country.

Such different figures are common in the immediate aftermaths of attacks in Syria. The reports could not be independently confirmed.

Al Jazeera’s Nisreen El-Shamayleh, reporting from neighbouring Jordan, said there were videos allegedly showing both children and adults in field hospitals, some of them suffocating, coughing and sweating.

"We have been receiving reports that the doctors in the field hospitals do not have the right medication to treat these cases and that they were treating people with vinegar and water,” she said.

The head of the UN chemical weapons inspectors in Syria said that reports of the gas attack should be investigated.

Swedish scientist Ake Sellstrom told news agency TT that while he had only seen TV footage, the high number of casualties reported sounded suspicious.

The opposition Syrian National Coalition has called for an urgent UN Security Council meeting after the deadly attack.

"I call on the Security Council to convene urgently,” National Coalition leader Ahmed al-Jarba told Al-Arabiya news channel, condemning the Syrian army’s bombardment of the Ghouta suburbs of Damascus as a "massacre.”

He urged the UN commission of inquiry on the use of chemical weapons to visit the site.

In Cairo, the Arab League urged UN inspectors now in Syria to visit the site of the alleged attack immediately.

UK said it would raise the reported chemical weapons attack by forces loyal to Syrian President Bashar Al-Assad at the United Nations Security Council and called on Damascus to give UN inspectors access to the site.

"I am deeply concerned by reports that hundreds of people,including children, have been killed in airstrikes and a chemical weapons attack on rebel-held areas near Damascus,” British Foreign Secretary William Hague said in a statement.

France will also ask UN experts to visit site of alleged chemical attack in Syria, French government spokesman said. 

Agencies