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.br br The two groups quote activists as saying that regime forces fired "rockets with poisonous gas heads" in the alleged attack early on Wednesday.br br The Britain-based Syrian Observatory for Human Rights says the shelling was intense and hit the eastern suburbs of Zamalka, Arbeen and Ein Tarma.br br Al Jazeera's Omar Al Saleh reports.