Two US F-22 stealth fighters intercepted two Russian aircraft Wednesday after the Russian jets crossed the Euphrates River in Syria, flying east of the "de-confliction line" that is supposed to separate Russian and US-led coalition aircraft operating over Syria, two US defense officials told CNN.
The US jets fired warning flares during the intercept of the two Russian Su-25 close air support jets according to the officials after they crossed the de-confliction line multiple times.
One of the officials said a Russian Su-35 fighter jet was also involved and that the aerial encounter lasted "several minutes."
The official said that coalition officers called their Russian counterparts about the incident via the pre-established de-confliction hotline.
US Air Forces Central Command told CNN last week that Russian aircraft had crossed the de-confliction line near the Euphrates River six to eight times a day in late November, something that US officials said prompted concerns of a clash between coalition and Russian aircraft.
"The greatest concern is that we could shoot down a Russian aircraft because its actions are seen as a threat to our air or ground forces," Lt. Col. Damien Pickart, the spokesman for US Air Forces Central Command, told CNN last week.
"As coalition leaders have repeatedly said, we're here to fight IS -- not the Russians or anyone else," he added.
President Donald Trump and Russian President Vladimir Putin pledged to continue to uphold those de-confliction measures in their recent joint statement issued on the sidelines of the APEC conference in Da Nang, Vietnam.
The statement said Trump and Putin "agreed to maintain open military channels of communication between military professionals to help ensure the safety of both US and Russian forces and de-confliction of partnered forces engaged in the fight against IS."
Officials have said that part of that arrangement involves defining where Russia and US aircraft operate, with those operations historically being separated by the Euphrates River, which runs through Syria, with US-backed forces operating to the east of the river and Russian/regime forces to the west.
America's top military officer, Joint Chiefs of Staff Chairman Gen. Joseph Dunford, spoke on the phone last week with his Russian counterpart, Gen. Valery Gerasimov, according to a spokesman for the Joint Staff.
Several US officials told CNN that de-confliction and operations in Syria were part of the discussions.