Vladimir Putin has sent his fearsome new state-of-the-art Su-57 stealth fighters for combat trials in the Syrian war zone.

Two of the fifth generation Sukhoi warplanes were spotted landing at Russia's Khmeimim Air Base, south-east of the city of Latakia.

The aircraft made its maiden flight in December last year and there was surprise at its deployment in Syria during its testing phase.

Putin has backed Syrian dictator Bashar al-Assad in his battle against rebels and jihadists in the country.  Assad's forces have launched a devastating bombing raid on rebel-held positions in eastern Ghouta in recent days, killing more than 300.