(CBS NEWS) -- Russia, Syrian President Bashar Assad’s most important backer on the world stage, condemned early Friday a U.S. missile strike on a Syrian airbase as “an aggression against a sovereign state in violation of international law.”

Russian President Vladimir Putin’s spokesman Dmitry Peskov said in a statement that Putin believes President Trump ordered the strikes under a “far-fetched pretext,” and Russia’s military announced it would reduce cooperation with the U.S. and bolster Assad’s air defenses in response.

In a post later Friday on social media, Russian Prime Minister Dmitry Medvedev said the U.S. strike had put America’s military “on the verge of fighting” directly with Russia’s. 

President Trump gave the command on Thursday for U.S. warships to fire a salvo of 59 Tomahawk cruise missiles at the Shayrat airfield in Syria’s Homs province.

American military officials say a Syrian jet, flying from Shayrat, carried out the Tuesday morning chemical weapons attack on the rebel-held town of Khan Sheikhoun. That attack left more than 80 people dead, including many children, and involved the deadly nerve agent Sarin gas, according to autopsies carried out in Turkey.

Syria’s army on Friday decried the U.S. strike as “an outrageous aggression.”  CBS News correspondent Jonathan Vigliotti says Syrian officials described the strike, however, as “limited and expected.” 

The damage to the airstrips, munitions and command and control infrastructure at the base was said to be significant.

Syrian dictator Bashar Assad has denied carrying out the chemical attack on Tuesday, saying any chemical agents released were from a rebel stockpile hit in conventional strikes carried out by Syrian warplanes. Russia backed up that explanation, and continued Friday to argue that rebel chemical weapons capabilities were being ignored.

On Friday, Assad labeled the U.S. strike “reckless” and “irresponsible.” In a statement he said the strikes were “shortsighted” and reflect a continuation of U.S. policy based on targeting and “subjugating people.” He said the decision to carry out the strike was not based on facts.

CBS News’ Holly Williams reports that several rebel groups have expressed relief -- hoping the U.S. missile salvo will reduce the ferocity of Syrian and Russian strikes against them on the ground -- but they’re not optimistic the U.S. government will offer more robust, direct support to them in the fight against Assad.

Experts refute the claim that a conventional strike would have dispersed chemical weapons, saying such a strike would instead have destroy the toxic chemical agents. In addition, chemical weapons experts say a conventional strike on a chemical stockpile wouldn’t have produced the harrowing scenes that have been broadcast around the world: People with no visible wounds, foaming at the mouth and suffocating to death.

Mr. Trump said he authorized the airstrike because “it is in the vital, national security interest of the United States to prevent and deter the use of deadly chemical weapons.”

Syria’s military said Friday that six soldiers were killed and several more wounded in the strike, and it declared the U.S. a “partner with ISIS, Nusra, and other terrorist groups” for launching an attack against Syrian forces. In a video statement, a Syrian commander said his forces would respond to the attack by continuing to “fight terrorism” wherever it exists.

How Russia reacts to Mr. Trump’s first major foreign military intervention as president -- and the first ever U.S. attack directly against the Assad regime -- will likely shape the next chapter in the Syrian war, in which the American role has just changed.

Russian countermeasures

“The actions taken today by the U.S.A. further destroy Russian-American relations,” Russia’s Foreign Ministry said Friday morning.

The message comes just days before U.S. Secretary of State Rex Tillerson is due to visit Moscow, where the Syria war will be just one of the areas of friction between the two countries. On Thursday, Tillerson said, “either Russia has been complicit or Russia has been incompetent” in allowing the Syrian regime to carry out the chemical attack. 

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