Syrian state television said government soldiers found chemical agents in rebel tunnels in the Damascus suburb of Jobar on Saturday and some of the troops were suffocating.
"Army heroes are entering the tunnels of the terrorists and saw chemical agents," state television quoted a "news source" as saying. "In some cases, soldiers are suffocating while entering Jobar," it said.
"Ambulances came to rescue the people who were suffocating in Jobar," it said, adding that an army unit was preparing to storm the suburb where rebels fighting to oust President Bashar al-Assad are based.
Syrian activists accuse Assad's forces of launching a nerve gas attack in Jobar and other suburbs before dawn on Wednesday, killing between 500 and more than 1,000 people.
Assad's government has dismissed the accusation and its major ally Russia has suggested rebel fighters may have launched the attack themselves to provoke international action.
U.N. High Representative for Disarmament Affairs Angela Kane arrived in Damascus on Saturday to push for access to the suspected chemical weapons attack site for U.N. inspectors, who are already in Syria to investigate months-old accusations.
So far Assad's government has not said whether it will allow access to the site despite being under increasing pressure from the United Nations, Western and Gulf Arab countries and Russia. If confirmed, it would be the world's deadliest chemical attack in decades.