MOSCOW (REUTERS) - Just under half of Russia's fixed-wing strike force based in Syria has flown out of the country in the past two days, according to a Reuters calculation based upon state TV footage.

Analysis of satellite imagery, footage of Russian air strikes, and defence ministry statements have previously suggested that Russia kept around 36 military jets at its Hmeymim base in Syria's Latakia province.

Analysis of state TV footage shows at least 15 of those planes, including Su-24, Su-25, Su-30 and Su-34 jets, have taken off for Russia in the past two days.

Reuters could not independently verify the movements of the aircraft. It was impossible to determine if other aircraft were flying in to Syria to replace those that left.

Russia is also known to maintain at least 14 military helicopters as well as fixed-wing reconnaissance drones at the base. If they are pulled out, the helicopters are likely to be shipped out by sea or by air.

Russian President Vladimir Putin announced out of the blue on Monday that "the main part" of the Russian military contingent in Syria would start to withdraw.