Iran on Sunday condemned allegations of a chemical attack on Syria's Eastern Ghouta rebel holdout as a "conspiracy" against its ally President Bashar al-Assad and a pretext for military action.
"Such allegations and accusations by the Americans and certain Western countries signal a new conspiracy against the Syrian government and people, and a pretext for military action," Iran's foreign ministry said in a statement.
Tehran warned any military intervention would "certainly complicate the situation" in Syria and the wider region.
"With the Syrian army having the upper hand on the ground against the armed terrorists, it would not be rational for it to use chemical weapons," the statement said.
An alleged chemical attack that left dozens dead in Syria's rebel-held town of Douma has sparked international outrage, with US President Donald Trump warning there would be a "big price to pay".
The Syrian regime and its other key backer Russia both denied any use of chemical weapons as "fabrications".