The regime's most powerful ally dismissed criticism of its intervention from Western states, which are carrying out air strikes on jihadists in both Syria and neighbouring Iraq, although they also seek Assad's ouster.
"We helped, are continuing to help and will help the Syrian government when it comes to supplying the Syrian army with everything it needs," said Russian Foreign Minister Sergei Lavrov.
Islamic State group jihadists edged closer to a strategic airbase outside the eastern city of Deir Ezzor in heavy clashes that left 54 combatants dead, said the Syrian Observatory for Human Rights.
Observatory director Rami Abdel Rahman said 36 IS fighters and 18 regime soldiers were killed.
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IS fought its way to barely one kilometre from the airport with the seizure of the army post used by a rocket battalion.
Two suicide bombers were used by the jihadists in the assault, one of them a child, driving cars laden with explosives, said Abdel Rahman.
IS already controls most of oil-rich Deir Ezzor province including about half of its capital, and has fought for more than a year to capture the airport and the rest of the city.
The Deir Ezzor assault came as rival jihadists from Al-Qaeda's Syrian affiliate and their allies yesterday seized the last regime-held military base in the northwestern province of Idlib.
According to the Observatory, the regime is now left with just three airbases in the east and north of the country -- Deir Ezzor, and Neirab and Kweyris in Aleppo province -- although it has military airports in other parts of Syria.
At least 56 soldiers were killed, some execution-style, as rebels captured Idlib's Abu Duhur military airport under the cover of an intense sandstorm following a two-year battle, the Observatory said.
Rebels tweeted images of helicopters and planes abandoned on the tarmac.