President Vladimir Putin ordered "a significant part" of Russia's military contingent in Syria to start withdrawing yesterday, saying Moscow and Damascus had achieved their mission of destroying Islamic State in just over two years.

Putin, who polls show will be re-elected comfortably in March, made the announcement during a surprise visit to Russia's Hmeymim airbase in Syria, where he held talks with President Bashar al-Assad and addressed Russian forces.

The Kremlin first launched air strikes in Syria in September 2015 in its biggest Middle East intervention in decades, turning the tide of the conflict in Assad's favour, while dramatically increasing Moscow's own influence in the region.

Syrian state television quoted Assad as thanking Putin for Russia's help, saying the blood of Moscow's "martyrs" had been mixed with the blood of the Syrian army.

Russia's campaign, which has been extensively covered on state TV, has not caught the imagination of most Russians. But nor has it stirred unease of the kind the Soviet Union faced with its calamitous 1980s intervention in Afghanistan.

The use of private military contractors, something which has been documented by Reuters but denied by the defence ministry, has allowed Moscow to keep the public casualty toll fairly low.

Russia's "mission completed" moment in Syria may help Putin increase the turnout at the March presidential election by appealing to the patriotism of voters.