Syria's government had said Turkish forces were believed to be among 100 gunmen who entered Syria on Saturday with 12 pick-up trucks mounted with heavy machine guns, in an operation to supply insurgents fighting Damascus.

Turkey's army shelled Kurdish YPG militia targets in northern Syria over the weekend, after the group seized an air base north of Aleppo, further complicating the conflict on NATO-member Turkey's southern border.

Ankara regards the YPG as a terrorist organisation and an extension of the Kurdistan Workers Party (PKK), which has fought a 31-year-old insurgency for autonomy in southeast Turkey.

Washington, which does not see the YPG as terrorists, backs the group in the fight against Islamic State in Syria.

Prime Minister Ahmet Davutolgu has demanded that the YPG withdraw from areas it has captured from Syrian rebels.

US President Barack Obama urged Russia yesterday to stop bombing "moderate" rebels in Syria in support of its ally President Bashar al-Assad, a campaign seen in the West as a major obstacle to efforts to end the war.

Yilmaz also denied reports that Saudi Arabian aircraft had arrived at Turkey's Incirlik air base for the fight against Islamic State militants, but said a decision had been reached for Saudi to send four F-16 jets.

A Turkish soldier was killed on Sunday evening after Turkey's security forces clashed with a group at the Syrian border that was trying to enter Turkey illegally, the armed forces said in a statement.

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