Russian Defense Ministry spokesman Igor Konashenkov said today that Su-35 fighters have been deployed to Hemeimeem air base in Syria.
Konashenkov today didn't say how many Su-35s had been sent to Syria, but Russian media reports said there were four of them and state television showed them parked in Hemeimeem.
Russian warplanes so far have flown about 6,000 missions since Moscow launched its air campaign four months ago.
The Kremlin says its planes have struck the Islamic State group and other extremists, but the US and its allies have accused Russia of also targeting moderate opposition groups.
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The negotiations are intended to pave the way for a new constitution and new elections in a year and half. Konashenkov said Russian warplanes flew 468 combat missions last week alone.
He said that all Russian strike aircraft are now being accompanied by Russian or Syrian fighter jets.
Russia added fighter escorts after a Turkish fighter jet downed a Russian bomber at the border with Syria on November 24.
The downing of the Russian jet was the first time in more than half a century that a NATO member had shot down a Russian plane.
The incident badly strained previously close ties between the two countries, with Moscow slamming Turkey with an array of economic sanctions.
Turkey said another Russian warplane violated its airspace Friday, and Turkish President Recep Tayyip Erdogan warned Moscow that it would be forced to "endure the consequences" if its jets continue to violate Turkish airspace.