Story highlights Russian statement comes day after US Navy jet shoots down Syrian warplane

Defense official: Threat level has escalated in Syria

Moscow (CNN) A day after a US Navy fighter jet shot down a Syrian warplane, Russia warned that aircraft operating where the shootdown occurred would be considered "air targets" for its forces in Syria.

The Russian Ministry of Defense called the downing of the plane "a cynical violation of the sovereignty of the Syrian Arab Republic" and "military aggression."

As a result, it said, Russia has stopped using a key "de-confliction" communication channel set up to avoid conflict between US and Russian forces in Syria.

While both the US and Russia say their forces are in Syria to fight ISIS infiltration there, Russia has allied itself with the regime of Syrian President Bahsar al-Assad while the US-led coalition has aligned with groups that oppose both the Assad regime and ISIS.

Russian Deputy Foreign Minister Sergei Ryabkov said Monday the US shootdown of the Syrian Su-22 was "an act of assistance to those terrorists whom the United States is ostensibly fighting against," according to Russia's state-run news agency Tass.

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