Iran, the chief regional ally of Damascus, said on Saturday there is "proof" Syrian rebels used chemical weapons in their conflict with the regime of President Bashar al-Assad.
"We are very concerned about information regarding the use of chemical weapons in Syria, and we strongly condemn the use of such weapons," foreign ministry spokesman Abbas Araqchi said, quoted by ISNA news agency.
"There is proof terrorist groups carried out this action," Araqchi said in reference to Wednesday's allegedly deadly attacks in the Damascus area, without elaborating.
President Hassan Rowhani on Saturday also pointed to the use of chemical weapons in Syria, but without assigning blame.
"The situation prevailing in Syria today and the death of a certain number of innocent people caused by chemical weapons is very distressing," he said, according to a government website.
Rowhani added that Iran, itself a victim of chemical attacks in its 1980-1988 war with Iraq, "totally and vigorously condemned the use of chemical weapons".
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During the conflict, chemical strikes by the Iraqi armed forces killed thousands of Iranians, particularly in civilian areas.
Araqchi warned against any Western military intervention in Syria's 29-month conflict, after the United States suggested it was weighing up such a possibility.
"There is no international authorisation for a military intervention in Syria. We warn against any actions or statements that could create more tension in the region. I hope that White House officials show enough wisdom not to enter into such dangerous tumult," Araqchi added.
Syria's main opposition body, the National Coalition, has accused Assad's regime of "massacring" more than 1,300 people in chemical weapons attacks on the outskirts of Damascus on Wednesday, which the regime has categorically denied.
"The provocative words of American officials or sending warships do not help to solve the problem in any way, but make the situation in the region more dangerous," said Araqchi.
Iran is Damascus's key ally in the region, and regularly warns against boosting Sunni Muslim extremist groups linked to Al-Qaeda that are fighting in the country.