Iranian President Hassan Rouhani affirmed his support for Syrian President Bashar al-Assad's government on Sunday, following last week's United States missile strike on a Syrian airbase.

In a phone call with Assad, Rouhani called the strike on Friday a "blatant violation" of Syrian sovereignty, Syrian state media reported. Assad accused the US of trying to boost the morale of "terror groups" in Syria.

The US says the strike was in response to a nerve gas attack on the rebel-held town of Khan Sheikhoun last week, which has been widely blamed on government forces. The Syrian government has denied using chemical weapons.

US Secretary of State Rex Tillerson denied in an interview that the strikes signaled an overhaul of American policy, saying its priority remained to defeat Islamic State.

Meanwhile, Turkish Foreign Minister Mevlut Cavusoglu on Sunday played down concerns of a rift with Russia over Ankara's support for the strike, saying Turkey was committed to the cease-fire mechanisms it has developed with Russia for Syria.

But he said Turkey could not "remain silent" on chemical weapons use, and insisted Moscow work with Ankara to establish a transitional government in Damascus.