Vladimir Putin believes that the US strike on a Syrian air base is an "aggression against a sovereign state in violation of international law", the Kremlin has revealed.
The Russian President thinks Donald Trump launched the attack under "far-fetched pretext", his spokesman Dmitry Peskov said in a statement.
The US President launched 59 missiles at the Syrian base from which this week's gruesome chemical attack is thought to have originated, leaving five dead and seven wounded. It's a move that has put him on a collision course with Putin, ending the two world leaders' relatively cordial relationship.
Russia has argued that the death of civilians in the Syrian town of Khan Sheikhoun on Tuesday resulted from Syrian forces hitting a rebel chemical arsenal there. Peskov said the US has previously ignored the use of chemical weapons by Syrian rebels and that the Syrian government has destroyed its chemical weapons stockpiles under international control.
Konstantin Kosachev, head of the foreign affairs committee in the Kremlin-controlled upper house, said the prospective US-Russian anti-terror coalition has been "put to rest without even being born."
He called the attack that almost destroyed Shayrat military base near Homs, in the country's west, "a pity", suggesting the US President had been pressured into the act by the Pentagon.
"Russian cruise missiles strike the terrorists, US missiles strike Syrian government forces who are spearheading the fight against the terrorists," he added.
A US defence official said Russians were present at the base, and the US military contacted its Russian counterparts about the attack ahead of time. But this does not appear to have been enough to prevent the icing over of relations.
Trump's core supporters in the US also turned on him over his change of attitude towards Syria, with right-wing commentators declaring themselves "OFF the Trump train".
US pundits hazarded that President Bashar al-Assad "must be stunned" at the huge missile strike.
The Syrian regime has been "carrying out mass atrocities against Syrian civilians at will" for years, wrote Dexter Filkins in the New Yorker, and only now has a punishment been meted out.
Trump's former fiercest detractors took the extraordinary step of praising the US President.
An editorial in the New York Times, habitually engaged in a war of words with the unpredictable commander-in-chief,said Mr Trump was "right to strike" and "should be commended".
The Wall Street Journal said the President had "demonstrated a comfort with military action and a flexibility in approach that saw him change course" on Syria just 48 hours after horrific images of the 80 civilians killed in chemical attacks emerged.