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 said Donald Trump launched the attack under "far-fetched pretext", according to a statement from his spokesman Dmitry Peskov, news.com.au reported.
The Russian Foreign Ministry said in Friday's statement that Moscow is suspending a bilateral agreement with the US that prevents midair collisions over Syria.
The memorandum, signed by Russia and the US in 2015, allowed both countries to exchange information about their flights to avoid incidents in the crowded skies over Syria.
Russia has several dozen warplanes and batteries of air-defence missiles at its base in Syria.
The suspension of the deal comes after the US launched 59 missiles at the Syrian base where this week's gruesome chemical attack is thought to have originated. The Syrian military is reporting at least seven people have been killed and several more injured, according to the Associated Press.
It's a move that has put Trump 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.
Mr 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.
Mr 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.
WHAT IS THE 'DECONFLICTION LINE'?
A communication link between U.S. and Russian military officials has protected pilots flying missions over the crowded skies of war-ravaged Syria, but now Moscow says it is suspending its cooperation over an American missile strike.
The following is an explanation of the so-called "deconfliction line" and the possible consequences of cutting it.
FLYING THE UNFRIENDLY SKIES
A US-led coalition has been bombing Islamic State-held territory across Syria, launching 24 strikes on Thursday alone, according to the U.S. military's Central Command. The coalition includes some 60 countries, with some launching their own strikes into Syria.
Russia is waging its own bombing campaign in support of President Bashar Assad's forces, while the Syrian government has its own air force and air defense systems. That means a lot of aircraft are flying in a small airspace, which raises the danger for pilots. In November 2015, for instance, NATO member Turkey shot down a Russian jet fighter, nearly sparking an international conflagration.
WATCHING THE WAR FROM QATAR
To protect pilots, Russia and the U.S. opened a so-called "deconfliction line" in late 2015. On the U.S. side, it is run out of the Combined Air and Space Operations Center at the vast al-Udeid Air Base in Qatar, which hosts the forward headquarters of U.S. Central Command. There, air traffic controllers and senior military officers are in contact with their Russian counterparts in Syria. They share coordinates and other data to avoid midair collisions or confrontations. One U.S. pilot flying missions over Syria credited his safety to it in a recent Associated Press interview .
MISSILE STRIKES AND NEW WARNINGS
On Thursday, US President Donald Trump ordered a missile strike on the Shayrat air base, southeast of Homs, over a chemical weapons attack he blamed on Syria's government. The US used the "deconfliction line" to warn Russia ahead of time that the strike was coming. In the aftermath of the attack, which Syria said killed at least seven people, Russia announced it would suspend its cooperation in the information-sharing campaign. Russia still has several dozen warplanes and batteries of air defense missiles at its base near Latakia, Syria.
WHAT HAPPENS NEXT
US Central Command and the Pentagon did not immediately respond to requests for comment over the Russian decision. The U.S. maintains radar coverage and has other surveillance means to know who is in the air. However, ending the cooperation will mean U.S. and coalition pilots will be flying into Syrian airspace not knowing if Russian forces plan their own operations in the same places. Airwars, a nonprofit monitoring airstrikes in the war against the Islamic State group, noted that US-led attacks typically focus on areas away from Russian activity, though ending the cooperation represents "a worrying development."