Syria's government has said Turkish shelling of northern Syria amounts to direct support for rebel groups, Syrian state TV has reported, citing a letter to the United Nations.
In recent days, Turkey has targeted areas including an airbase captured by the Syrian Kurdish YPG alliance.
The country's prime minister Ahmet Davutoglu has threatened retaliation "against every step" if the YPG do not leave the airbase.
Russian President Vladimir Putin and US President Barack Obama discussed issues related to resolving the conflict in Syria on Sunday, the Kremlin has said.
During phone talks, both leaders agreed to intensify diplomatic and other cooperation to implement a ceasefire agreed at a global security conference in Munich, the Kremlin said in a statement.
The Turkish army have shelled positions held by Kurdish-backed militia in northern Syria for a second day, killing two fighters, the Syrian Observatory for Human Rights monitoring group has said.
On Saturday, Turkey demanded the Syrian Kurdish YPG militia withdraw from areas that it captured in the northern Aleppo region in recent days.
The shelling has targeted an air base and other positions captured by the Kurdish-backed forces from insurgents in Syria.
Turkish prime minister Ahmet Davutoglu warned that Turkey would retaliate if the YPG did not leave the airbase.
"We will retaliate against every step. YPG and the forces behind it should be aware of Turkey's stance. The YPG will immediately withdraw from Azaz and the surrounding area and will not go close to it again", he said.
Russia has been accused by its western allies of jeopardising peace in Syria by bombing the wrong targets as a recently agreed ceasefires hangs in the balance.
But Russian Prime Minister Dmitry Medvedev has spoken during a security conference in Munich to deny that Russian forces are bombing civilians.
ITV Political Correspondent Paul Brand reports:
Philip Hammond appeared to be unimpressed with Russia's response to the accusations that the country's forces have bombed civilians, rolling his eyes as Russian Foreign Minister Sergei Lavrov defended his country's actions.
The Foreign Secretary shook his head and looked to the sky as Lavrov spoke at a security conference in Munich about how "moving closer to practical goals of truce" would not work without co-operation between military forces.
US Secretary of State John Kerry has accused Russia of hitting legitimate opposition groups and civilians with its bombing campaign in Syria.
Speaking at a security conference in Munich, Mr Kerry said Moscow must change its targets in order to respect a ceasefire deal agreed on Friday.
To date, the vast majority of Russia's attacks have been against legitimate opposition groups. To adhere to the agreement it made, Russia's targeting must change.
He also said Moscow had been dropping so-called "dumb bombs" that do not have a precise target, leading to the killing of civilians.
Earlier, Russian Prime Minister Dmitry Medvedev rejected claims Russia has bombed civilians in Syria, saying: "There is no evidence of our bombing civilians, even though everyone is accusing us of this."
French Prime Minister Manuel Valls has called on Russia to stop bombing civilians in Syria, saying it is crucial for achieving peace in the country.
In a speech at a security conference in Munich, Mr Valls said: "France respects Russia and its interests ... But we know that to find the path to peace again, the Russian bombing of civilians has to stop".
Russian Prime Minister Dmitry Medvedev rejected claims Russia has bombed civilians in Syria, saying there was "no evidence" to back the accusations.
Tensions between Russia and the West have plunged the world into a "new Cold War", Dmitry Medvedev has said.
The Russian Prime Minister said his country was "accused of making new horrible threats either against NATO as a whole, against Europe or against the US or other countries" on an almost daily basis.
Relations between Russia and the West have been strained by the Ukraine conflict and Russia's backing of Bashar al-Assad's regime in Syria.
Speaking at the Munich Security Conference, Mr Medvedev said: "We can say it even more clearly: We have slid into a new period of Cold War."
He said the US and Russia needed to cooperate regularly to resolve the crisis in Syria.
Mr Medvedev also rejected claims Russia has bombed civilians in Syria, saying there was "no evidence" to back the accusations.
Saudi Arabia's foreign minister has insisted Bashar al-Assad will not be ruling Syria in the future, and that Russian intervention in Assad's favour is in vain.
Adel al-Jubeir's comments come in an interview with the German newspaper newspaper Sueddeutsche Zeitung, published on Saturday.
"It might take three months, it might take six months or three years - but he [Assad] will no longer carry responsibility for Syria. Period," al-Jubeir said.
Saudi Arabia has long said that the Syrian president must step down if Syria's conflict is to end.
The people of Aleppo in Syria are going to take some convincing that a truce will actually happen.
Much of the city is in ruins after five years of fighting and President Bashar al-Assad is making rapid ground with his Russian-backed assault.
Many continue to flee the war-torn country, for whom any ceasefire would come too late.
ITV News Middle East Correspondent Geraint Vincent reports: