The US missile strikes on a Syrian military base crossed “red lines” according to Russia and Iran, who have threatened to respond with force to similar action.
In a joint statement, allies of President Assad’s government described the strikes – carried out in response to a chemical attack on civilians – as an aggression on Syria.
The Russian and American foreign ministers are due to meet in Moscow this week.
On Friday Russia warned the move would further damage ties with Washington.
On Sunday the US Secretary of State Rex Tillerson questioned Russia’s motives in Syria, saying it had failed to prevent Damascus from carrying out a chemical attack on a rebel-held town.
“Clearly they are Bashar al-Assad’s current ally, they should have the greatest influence on Bashar al-Assad and certainly his decisions to use chemical weapons, they should have the greatest influence on him, to cause him to no longer use those. I hope that Russia is thinking carefully about its continued alliance with Bashar al-Assad because every time one of this horrific attack occurs, it draws Russia closer in to some level of responsibility,” Tillerson said in a TV interview.
Turkey, which welcomed the US strikes, joined in the criticism of Russia on Sunday.
Its Foreign Minister Mevlut Cavusoglu said he had told his Russian counterpart that Moscow had failed to prevent breaches in the Syrian ceasefire.
As the issue echoed across the Middle East, Iran’s President Rouhani slammed Donald Trump on Sunday for attacking Syria without UN backing
“How does the US president allow himself to attack an independent country in the sensitive region of the Middle East… without the permission of the United Nations, without a meeting of the UN Security Council and even without the permission of the US Congress?” Rouhani asked during a ceremony to mark Iran’s National Day of Nuclear Technology.
The Iranian leader also criticised other countries in the region for supporting the US action, saying “your turn will come too”.
Saudi Arabia as well as Turkey welcomed the US attack.