A host of Iranian leaders and officials have condemned the Western missile attack on Syrian targets in retaliation for the use of chemical weapons by Bashar Assad's forces.
Iran's Supreme Leader Ayatollah Ali Khamenei said coordinated air strikes on Syria by the United States, France and Britain on Saturday were a crime that would bring no benefit.
"Today's dawn attack on Syria is a crime. I clearly declare that the president of the United States, the president of France and the British prime minister are criminals," Khamenei said in a speech, according to his Twitter account.
Iran -- the dominant Shi'ite Muslim power which is in rivalry with Saudi Arabia and the United States' other Sunni Arab allies -- has been Syrian President Bashar al-Assad's most supportive ally against insurgents throughout the conflict.
Militias backed by Tehran helped Assad's army stem rebel advances and, following Russia's entry into the war in 2015, turn the tide decisively in the Syrian government's favor.
Gulf Arab counties, Israel and the West have accused Iran of trying to expand its influence in the region and threaten its neighbors.
Iran's pragmatist President Hassan Rouhani warned that the U.S.-led missile attacks would lead to further destruction in the Middle East, the semi-official Tasnim news agency reported.
"Such attacks will have no result but more destruction ... the Americans want to justify their presence in the region by such attacks," Rouhani was quoted as saying, signalling that Iran's support for Assad would grow.
An official in Iran's Revolutionary Guards Corps (IRGC), the Islamic Republic's most powerful arm, said fallout from the attacks would harm Washington.
"With this attack ... the situation will become more complex, and this will surely be at the expense of the United States, which will be responsible for the aftermath of upcoming regional events that will certainly not be in their interest," Yadollah Javani, the Guards' deputy head for political affairs, told Fars news agency.
In a statement, the IRGC said: "This unrelenting confrontation shows that the Syrian people, with the support of the strategic allies of Damascus, will not stop until achieving complete victory," Fars reported.
The IRGC and its Qods force have been assisting Lebanese Hezbollah for more than three decades and more recently have been supporting Yemen's Houthi rebels and Shiite militias in Iraq. Many of their leaders, institutions and companies linked with it have been sanctioned by the West .
Iran's military chief of staff General Mohammad Baqeri assured Syrian Defense Minister Ali Abdullah Ayoub of Tehran's continued support. "The nation and the armed forces of the Islamic Republic of Iran will continue to fight alongside the Syrian people and the Syrian armed forces against the criminal terrorists," Fars quoted Baqeri as telling Ayoub by telephone.
Earlier, the Foreign Ministry in Tehran said Washington and its allies had attacked Syria "despite the absence of any proven evidence." "Iran is opposed to the use of chemical weapons on the basis of religious, legal and ethical standards, while at the same time it ... strongly condemns (using this) as an excuse to commit aggression against a sovereign state," it said in a statement carried by state media.