Russian Federation made clear it was changing its military posture in response to the USA downing of a Syrian military jet on Sunday, something Damascus said was the first such incident since the start of the country's conflict in 2011.
USA -backed opposition fighters said Assad's forces have been attacking them in the northern province of Raqqa and warned that if such attacks continue, the fighters will take action.
The Russian defense ministry says in a statement that, starting Monday, it will track all jets and drones of the US -led coalition west of the Euphrates and treat them as targets.
A U.S. F-18 jet shot down a Syrian bomber on Sunday to protect USA allies fighting Islamic State, and on Monday Russia and Iran threatened to target US planes in response.
Syrian government forces have also been attacking IS in northern, central and southern parts of the country, seizing 25,000 square kilometers (9,600 square miles) and reaching the Iraqi border for the first time in years.
Areas of northern Syria west of the Euphrates were controlled by IS before Syrian government forces captured a lot of them in recent months.
The United States wants to re-establish a military hotline that Russian Federation said it had severed after an American jet shot down a Syrian regime warplane, the top U.S. general said Monday.More news: Iran calls missile attack on Syria militants a wider warning
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The remarks came amid questions whether the strike had been effective.
A United States official told AFP the pilot of the Syrian plane appeared to have ejected before the jet was hit, though his fate was unknown.
The truce that went into effect Saturday came after some of the worst fighting in months between rebels and pro-government forces. Israeli security officials said Monday they were studying the missile strike to see what they could learn about its accuracy and capabilities.
-Russian military "deconfliction" hotline in response to a USA shootdown Sunday of a Syrian fighter jet.
Speaking in Washington, the top USA military officer said the two sides were in delicate discussions to lower tensions.
Associated Press writers Rod McGuirk in Canberra, Australia, Albert Aji in Damascus, Syria and Nasser Karimi in Tehran, Iran, contributed to this report. Iran's powerful Revolutionary Guard, a paramilitary force in charge of the country's missile program, said it launched six Zolfaghar ballistic missiles from the western provinces of Kermanshah and Kurdistan.
Marine Corps General Joseph Dunford testifies during the Senate Armed Services committee nomination hearing to be chairman of the Joint Chiefs of Staff on Capitol Hill in Washington, July 9, 2015.
The American F/A-18E Super Hornet shot down the Syrian SU-22 around 7:00 pm as it "dropped bombs near SDF fighters" south of the town of Tabqa. -Russian understanding on avoiding air incidents.