International divisions over Syria have resurfaced at the Munich conference where Russia has rejected charges by France and the US it's bombing civilians.
US Secretary of State John Kerry says Russia is hitting legitimate opposition groups and civilians, and must change its targets to respect a ceasefire deal clinched in Munich on Friday.
But Russia, an ally of Syrian President Bashar al-Assad, insists it is battling terrorists.
Russia's Foreign Minister Sergei Lavrov told the security conference Russia is "not trying to achieve some secret goal in Syria", but is trying to protect their national interests".
He said some of the extremists in Syria are from Russia and would otherwise return to commit acts of terror.
Pressure is increasing on Russia over its bombing campaign in Syria.
French Prime Minister Manuel Valls and Mr Kerry said civilians are dying in the Russian air strikes.
They were speaking at a meeting of world leaders in Munich, days after they reached a deal on ending the fighting in Syria.
Mr Valls said an end to the bombing was crucial if there was to be peace.
Mr Kerry said Moscow must change its targets to respect a ceasefire deal clinched in Munich on Friday.
Syrian rebels might be pushed aside but they are not going to surrender, he said.
However, Russian Prime Minister Dmitri Medvedev said there was no evidence its airstrikes in Syria were affecting civilians.
Mr Medvedev said the strains between Russia and the west over Syria could push the world into a new cold war.
British Foreign Secretary Phillip Hammond said the moderate opposition in Syria will not join the peace process if Russia doesn't change its tactics.
Meanwhile, Syrian rebel groups said they would not stop fighting because they did not believe Russia would end its campaign in support of the government.
The rebels have expressed scepticism over Friday's deal by world powers to push for a cessation of hostilities within a week, and reiterated their demand that the President, Bashar al-Assad, be removed from power.
The president himself has said saying he wants to retake "the whole country" from rebels.
Turkey mulling ground invasion
Turkey has shelled a Kurdish militia in northern Syria and demanded it retreat from territory it has seized, Prime Minister Ahmet Davutoglu said.
The US urged Turkey to stop the shelling and focus on fighting the group Islamic State (IS).
Meanwhile Turkey's foreign minister said Turkey was mulling a ground invasion of Syria with Saudi forces.
On Thursday world powers agreed to push for a cessation of hostilities in Syria within a week.
Among the targets shelled by Turkey was the Menagh airbase, which was seized on Thursday from Syrian Islamist rebels by a Kurdish militia group known as the YPG.
Speaking on Turkish TV, PM Davutoglu warned that Turkey would retaliate if the YPG did not leave the airbase, which lies south of the town of Azaz and near the Turkish border.