The Russian military has beefed up its air group in Syria with state-of-the art fighter jets amid tensions with Turkey.

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.

Russian air strikes have helped Syrian President Bashar Assad's army win more ground in recent weeks. They have strengthened Assad's hand just as Syrian peace talks have got underway in Geneva.

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 Russian military has vowed to fend off any future threats to its warplanes with fighters and long-range air defense missiles at Hemeimeem.

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.

Konashenkov today denied the Turkish claim, adding that Ankara has failed to provide any proof.