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.