The Russian Defense Ministry has announced its intention to begin treating U.S. coalition jets flown west of the Euphrates River in Syria as air targets.
The announcement came after the U.S. shot down a Syrian regime fighter jet on Sunday, which the ministry called a "massive violation of international law," according to ABC News.
Russia said in response to the incident that it would target U.S.-led coalition jets in parts of Syria, the Associated Press reported Monday morning.
BREAKING: Russia says it will treat US-led coalition planes in Syria, west of the Euphrates, as targets after US downed Syrian jet.
— The Associated Press (@AP) June 19, 2017
The Syrian plane was shot down by a U.S. Navy fighter jet after attempting to bomb U.S.-allied coalition forces, according to the U.S. military. This was the first time that the U.S. has itself engaged in air-to-air conflict with Syrian aircraft since it joined the fight against the Islamic State in 2014.
Russia backs the regime of Syrian President Bashar al-Assad in the country's ongoing conflict, and has called the U.S. strike a violation of Syrian sovereignty.
"Repeated combat actions by U.S. aviation under the cover of counterterrorism against lawful armed forces of a country that is a member of the U.N. are a massive violation of international law and de facto a military aggression against the Syrian Arab Republic," the Russian Defense Ministry said.
The ministry added that any aircraft flying west of the Euphrates "will be tracked by the Russian ground and air anti-aircraft defense systems as air targets in the areas where Russian aviation is on combat missions in the Syrian sky."
Sunday's shoot-down occurred to the southwest of the Euphrates.
The Russian Defense Ministry also contradicted a U.S. claim that an air safety hotline had been used prior to the incident, and said that Russian planes were airborne at the time.
Moscow repeated an earlier promise to stop using the established deconfliction hotline between the U.S. and Russia in Syria. It has previously claimed it would do so following the U.S. missile strike on a Syrian air field in April as retaliation for a chemical weapons attack by the Assad government. Use of the hotline continued, however.
A statement from the coalition stressed that it will continue to defend U.S. allies.
"The coalition does not seek to fight Syrian regime, Russian, or pro-regime forces partnered with them, but will not hesitate to defend coalition or partner forces from any threat," the U.S. coalition said.
"The demonstrated hostile intent and actions of pro-regime forces toward coalition and partner forces in Syria conducting legitimate counter-ISIS operations will not be tolerated," it said.