The news circulated by the activists' media outlets, "which are partners in shedding the Syrian blood", are totally "baseless", media reported. (Agencies)
The claims aim to divert the attention of the visiting UN chemical inspection team from the original target of its mission, it added.
Earlier in the day, Syrian opposition activists posted online videos of dead people who they claimed were the "victims of the chemical attack", accusing the army of using "poisonous gases" in Damascus.
The accusation came at a time when the UN mission is in the country to investigate the possible usage of chemical weapons in the Syrian conflict. The probe was requested by the Syrian government, who accused the rebels of using "sarin agent" in the northern town of Khan al-Asal.
The Syrian government welcomed the arrival of the UN inspectors on Sunday, pledging to cooperate with them and facilitate their work. “Syria is fulfilling what we have agreed on with the international mission,” Prime Minister Wael Al-Halqi said.
"Our colleagues in the Foreign Ministry have prepared all the procedures in order to make their work a success,” he added.
The Prime Minister also accused Turkey of providing armed rebels with chemical weapons that were used in Khan al-Asal, near the city of Aleppo. The US and several European countries have expressed fears that Syria's chemical weapons may "fall into the wrong hands" if the Syrian administration falls.
Israel also said that it has intervention plans to secure the arsenals in case of a "regime collapse" in Syria.
650 dead in chemical bombing: Opposition
More than 650 people were killed in fierce Syrian army bombardment with chemical weapons of Damascus suburbs today, the opposition said, branding it a "massacre" and calling for international intervention.
Britain, meanwhile, said it would refer the alleged chemical weapons attack, which could not immediately be verified and has been vehemently denied by the Damascus regime, to the United Nations.
While the Syrian National Coalition gave a toll of 650 dead, a Britain-based monitoring group said earlier that at least 100 people had been killed and the number was rising.
"This figure will surely go up. The raids and bombardment are continuing," said the Syrian Observatory for Human Rights, which gathers its information from activists and medics.
The Syrian National Coalition called for an urgent UN Security Council meeting. "I call on the Security Council to convene urgently," National Coalition leader Ahmed al-Jarba said.
The news circulated by the activists' media outlets, "which are partners in shedding the Syrian blood", are totally "baseless", media reported.