Syrian President Bashar Assad said in comments broadcast on Sunday that the success of Russia's military intervention in his country's civil war was vital for the whole Middle East.

"The alliance between Russia, Syria, Iraq and Iran must succeed or else the whole region will be destroyed," he said in an interview broadcast by Iranian state television.

French Prime Minister Manuel Valls urged Russia on Sunday to direct air strikes at Islamic State jihadists alone in Syria, as the West raises concerns Moscow will target moderate rebel groups opposed to Syria's president.

Speaking to journalists on a visit to Japan, Valls said Russia should not "get the wrong targets", echoing the words of French President Francois Hollande to Russian President Vladimir Putin at a Paris summit on Friday.

Russia is backing "butcher" President Bashar al-Assad with airstrikes that are often not aimed at Islamic State (IS) fighters in Syria, Britain's Prime Minister David Cameron said Saturday.

Cameron said Russian forces were "making the situation worse" as they pressed a bombing campaign in the IS stronghold for a fourth day. 

Turkish President Recep Tayyip Erdogan on Saturday urged Russian counterpart Vladimir Putin to reconsider Moscow's bombing campaign in Syria, accusing the Russian military of turning a blind eye to the killing of dozens of civilians.

Speaking in an interview with Al-Jazeera Arabic, Erdogan expressed anger that whereas Moscow had informed Ankara it would be attacking Islamic State (IS) jihadists in Syria, it had in fact targeted moderate Syrian rebels.

Warring sides in Ukraine on Saturday began withdrawing tanks and smaller weapons from a buffer zone in the war-torn east a day after the leaders of France and Germany met Vladimir Putin for peace talks.

The announcement of the beginning of the small-weapons withdrawal came after Ukrainian President Petro Poroshenko voiced cautious optimism over the future of a peace deal but said the war was not over.

Russia bombed the Islamic State group's Syrian stronghold Saturday and vowed to press its aerial campaign despite criticism from Washington and its allies that its military action was strengthening the jihadists.

A long-time staunch backer of Syrian President Bashar Assad, Russia began sorties over its ally on Wednesday in what it said would be a prolonged bombing campaign against IS and other extremist groups.

The leaders of Russia, Ukraine, France and Germany agreed Friday to delay contentious local elections in Ukraine to ensure that they meet international standards, despite fighting having all but stopped in the country's separatist east.

Peace appears closer than ever in the 17-month conflict, which has plunged relations between Moscow and the West to post-Cold War lows, with the latest ceasefire called last month having largely been observed by both pro-Russian rebels and Ukrainian forces.

Only one in 20 Russian air strikes in Syria have targeted Islamic State (IS) fighters, Britain's Defense Secretary Michael Fallon said Saturday.

British intelligence services observed that five percent of the strikes had attacked the militant jihadist group, with most "killing civilians" and Free Syrian forces fighting against the regime of president Bashar Assad, Fallon told the Sun newspaper.

Russia carried out a third day of air strikes in Syria on Friday and said it had hit Islamic State's 'capital' as President Vladimir Putin faced mounting international criticism over his military campaign.

Moscow said it had bombed "an IS training camp" and a command post in the IS bastion f Raqa on Thursday, but on Friday it targeted rebel groups opposed to Syrian President Bashar Assad.

Turkish Prime Minister Ahmet Davutoglu on Friday accused Russia of targeting moderate Syrian rebels in its air strikes in Syria to prop up the regime of President Bashar Assad.

Speaking to Turkish reporters on his plane as he returned from the U.N. General Assembly in New York, Davutoglu rejected Moscow's insistence that its campaign of air strikes launched this week was aimed at Islamic State (IS) jihadists.