In a statement on Friday morning, Russian Prime Minister Dmitry Medvedev said that the US missile strike violated not only international, and added that the attack “was on the brink of military clashes with Russia.”

“Instead of their much-publicized thesis about a joint fight with a common enemy, Islamic State [IS, formerly ISIS/ISIL], the Trump administration has proven that it will fiercely fight against the legal government of Syria,” Medvedev wrote on his Facebook page.

Ealier in the day, the Kremlin released a statement according to which "President Putin views the U.S. strikes on Syria as aggression against a sovereign state in violation of the norms of international law and on a made-up up pretext. This step by Washington will inflict major damage on U.S.-Russia ties."

"President Putin views the U.S. strikes on Syria as aggression against a sovereign state in violation of the norms of international law and on a made-up up pretext," said a Kremlin statement. "This step by Washington will inflict major damage on U.S.-Russia ties."

Moscow suspended communication with U.S. forces designed to stop planes colliding over Syria. A Russian frigate carrying cruise missiles sailed through the Bosphorus Strait into the Mediterranean Sea, although there was no indication it was directly in response to U.S. action.

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Meanwhile, the International Committee of the Red Criss told Reuters that the situation in Syria "amounts to an international armed conflict" following U.S. missile strikes on a Syrian airbase.

"Any military operation by a state on the territory of another without the consent of the other amounts to an international armed conflict," ICRC spokeswoman Iolanda Jaquemet told Reuters in Geneva in response to a query.

"So according to available information - the U.S. attack on Syrian military infrastructure - the situation amounts to an international armed conflict."

Previous air strikes on Syrian territory by a U.S.-led coalition have been against only the militant group Islamic State, which is also the enemy of the Syrian government. Russia has carried out air strikes in tandem with its ally Syria since Sept. 2015, while Iranian militias are also fighting alongside the troops of Syrian President Bashar al-Assad. ICRC officials were raising the U.S. attack with U.S. authorities as part of its ongoing confidential dialogue with parties to the conflict, Jaquemet said, declining to give details.

The ICRC, guardian of the Geneva Conventions setting down the rules of war, declared Syria an internal armed conflict - or civil war, in layman's terms - in July 2012.

Under international humanitarian law, whether a conflict is internal or international, civilians must be spared and medical facilities protected. Warring parties must observe the key principles of precaution and proportionality and distinguish between combatants and civilians.