Beirut (AFP) - Russian air strikes in support of the Syrian government have killed more than 1,500 people, a third of them civilians, since they began two months ago, a monitor said Monday.

The Syrian Observatory for Human Rights said Russian raids that began September 30 have killed 419 Islamic State group fighters as well as 598 from Al-Qaeda affiliate Al-Nusra Front and other rebel groups.

But the raids also killed 485 civilians, including 117 children and 47 women, the Britain-based Observatory said.

Russia has long been a staunch ally of Syria's President Bashar al-Assad and has backed him throughout the uprising that began in March 2011.

It stepped up its support with an aerial campaign that it says targets IS jihadists and other "terrorists".

Syrian opposition forces accuse Moscow of targeting moderate and Islamist rebels rather than jihadists.

More than 250,000 people have been killed in Syria since March 2011, according to the Observatory.