Asked to respond to the shootdown of a Syrian fighter jet over Syria, White House press secretary Sean Spicer said the United States will protect its interests in Syria and will "do what we can" to keep open lines of communication with Russia and Syria.
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"And so we've gotta do what we can to work with partners and we're going to continue to keep an open line of communication with the Russians," Spicer said at an off-camera press briefing Monday.
Spicer added that the U.S. wants to de-escalate the situation in Syria "but will always preserve the right of self-defense."
"The escalation of hostilities among all of the factions that are operating there doesn't help anybody," said Spicer. "And so making sure that people understand while we want to de-escalate the situation there, that we have to understand that we will always preserve the right of self-defense."
The Russian Defense Ministry earlier blasted the U.S.'s action as a "massive violation of international law" and said it will begin treating U.S.-led coalition jets flying west of the Euphrates River in Syria as targets.
The ministry's comments Monday came after a U.S. Navy fighter jet on Sunday shot down a Syrian fighter jet that dropped bombs on rebel forces fighting ISIS in Syria.
It was the first time the U.S. has engaged in air-to-air combat in Syria, signaling an escalation of the conflict. It is is also the first time an American aircraft has shot down any other country's plane in air-to-air combat since 1999, when a U.S. Air Force F-16 shot down a Serbian Mig-29 during the Kosovo air campaign.
Russia, which is backing the Syrian regime in the civil war, slammed the U.S. action as a violation of Syria's 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 warned that any U.S.-led coalition 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."
The Syrian jet was downed in an area southwest of the Euphrates River. The U.S.-led coalition conducts missions west of the Euphrates River near Manbij and Al Bab, two towns retaken from ISIS by U.S.-backed rebel forces.
Later the U.S.-led coalition fighting ISIS announced that while it would continue striking at ISIS in Syria, it was re-positioning its aircraft in light of the heightened tensions in the wake of the Syrian jet's shootdown.
"As a result of recent encounters involving pro-Syrian regime and Russian forces, we have taken prudent measures to re-position aircraft over Syria so as to continue targeting ISIS forces while ensuring the safety of our aircrew given known threats in the battlespace," said Lt. Colonel Damien Pickart, a spokesman for U.S. Air Forces Central Command.
The coalition said in a statement released Sunday after the shootdown that its focus is on fighting ISIS, not the Syrian regime or Russian forces, but that it will not hesitate to defend coalition or partner forces coming under attack.
The downing occurred over the town of Ja'Din, south of Tabqa, which was recently retaken from ISIS by the Syrian Democratic Forces, an umbrella group of Syrian Kurdish and Arab rebel forces supported by the U.S. in the fight against ISIS.
The SDF came under attack from Syrian President Bashar al-Assad's forces around 4:30 p.m. local time. A number of SDF fighters were wounded in the assault, and the SDF soon left Ja'Din.
Navy F/A-18s from the aircraft carrier USS George H. W. Bush, operating in the eastern Mediterranean, conducted a show of force overhead by firing warning shots at the pro-regime forces that turned back their advance toward the town.
"Following the pro-Syrian forces' attack, the coalition contacted its Russian counterparts by telephone via an established deconfliction line to de-escalate the situation and stop the firing," said a statement from Operation Inherent Resolve, the U.S.-led coalition fighting ISIS.
"At 6:43 p.m., a Syrian regime SU-22 dropped bombs near SDF fighters south of Tabqah and, in accordance with rules of engagement and in collective self-defense of coalition partnered forces, was immediately shot down by a U.S. F/A-18E Super Hornet," the statement continued.
The Syrian pilot is believed to have ejected from the aircraft, according to a U.S. official.
But the Russian Defense Ministry contradicted the coalition's claim that the air-safety hotline was used and noted that there were Russian aircraft in the area when the Syrian plane was shot down.
The ministry said it would stop its participation in the deconfliction line, much as it did after U.S. cruise missile strikes in Syria in April. But at the time, U.S. and Russian forces continued to use the hotline despite Russia's announcement.
Ja'Din is approximately 2 kilometers north of an established deconfliction area.
The U.S.-led coalition in its statement stressed its goals in Syria and said it will defend its partnered forces.
"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," it 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."
The downing of the Syrian jet is the latest escalation between the U.S.-led coalition and pro-regime forces in the country.
Over the last four weeks, the U.S. has conducted three airstrikes on pro-regime forces backed by Iran that have moved into a de-confliction zone around the town of Tanf in southwestern Syria, where there is a coalition training base for local forces fighting ISIS.