A joint command center made up of the forces of Russian, Iran and allied militia alliance supporting Assad regime said the U.S. strike on a Syrian air base crossed "red lines" and it would now respond to any new aggression and increase their level of support to their ally.
"What America waged in an aggression on Syria is a crossing of red lines. From now on we will respond with force to any aggressor or any breach of red lines from whoever it is and America knows our ability to respond well," said the statement published by the group on media outlet Ilam al Harbi.
U.S. military presence in northern Syria is "illegal" and their aim to control area makes them "occupation" forces, the statement added.
In a separate statement, Kremlin said that Russian President Vladimir Putin and his Iranian counterpart Hassan Rouhani noted in phone call that "aggressive" U.S. actions against Syria are not permissible.
The two leaders also called for an objective investigation into an incident involving chemical weapons in Syria's Idlib and said they were ready to deepen cooperation to fight terrorism, the Kremlin said in a statement on its website.
The two presidents said that they are ready to deepen cooperation on fighting terrorism to ensure stability in Middle East.
The Kremlin said the phone call took place on Iran's initiative.