"If this recent approach is serious, it will translate to a return from the headstrong and wrong approach" the United States had adopted by threatening to attack Syria, Khamenei said in remarks on state television.
"The Islamic Republic of Iran is carefully monitoring developments, and with vigilance," he added.
Iran, a staunch supporter of the regime of Syrian President Bashar al-Assad, actively opposed threats by the United States and France to launch a military strike against Damascus.
Khamenei has repeatedly spoken against war on Syria, warning that a US intervention would spell "disaster" for the region, which he likens to "a gunpowder depot."
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Obama said it was too early to say if a Russian plan to secure Syria's chemical weapons could forestall US air strikes.
Meanwhile, France is pushing for a binding Security Council resolution requiring Syria to swiftly implement its pledge to give up its chemical weapons or face punitive action.