Meanwhile, the head of Iran's powerful Revolutionary Guards warned that a US strike would trigger "reactions beyond" Syria and would bolster extremism.
"As representatives of the Islamic Republic of Iran we declare our hostility for any attack or war against Syria," IRNA news agency quoted Allaeddine Boroujerdi, chairman of parliament's influential foreign policy committee, as saying.
US President Barack Obama yesterday said he was weighing "limited, narrow" action against Syria after US intelligence reports said President Bashar al-Assad's regime had gassed to death hundreds of women and children.
"Unfortunately the United States did not heed our warning," he said after heading a three-member delegation that met Assad.
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Diplomatic relations between Iran and the United States have been severed since 1980, and the Swiss embassy in Tehran handles US interests there.
Syria's government has denied using chemical weapons and has pointed the finger of blame at "terrorists" -- its term for rebels seeking to topple Assad.
Boroujerdi said Iran condemns the use of chemical weapons "by terrorist groups against the Syrian population."
Iran, Damascus's main regional ally, has issued stern warnings against any US-led military action targeting Syria, with the latest today by the head of the elite Revolutionary Guards.
"The fact that the Americans believe that military intervention will be limited to within Syrian borders is an illusion; it will provoke reactions beyond that country," Jafari was quoted as saying by ISNA news agency.
"Just as US interventions in the Islamic world (Afghanistan, Iraq) have bolstered extremism, so will an aggression on Syria reinforce extremism and, as in Iraq and Afghanistan, its results will be pain, massacre and the exodus of the innocent population," he added.
Supreme leader Ayatollah Ali Khamenei has said a strike on Syria would be a "disaster" for the region.