A Turkish assault on positions claimed by Kurdish fighters in northern Syria has continued into a second day.
On Saturday, Turkey began shelling the militia, which it says is linked to the banned Kurdistan Workers Party (PKK).
The YPG militia, which is based in Syria, has rejected a demand by Turkey to leave areas it has seized, saying Islamists would return if it left.
Turkey's assault is a new thread in an already-complex conflict that has drawn in competing regional powers.
On Thursday, world leaders agreed to work towards a so-called cessation of hostilities in Syria within a week.
The US and Russian presidents agreed in a "frank and business-like" phone call to work more closely to achieve this, the Kremlin said on Sunday.
Among the targets shelled by Turkey is the Menagh airbase, which was seized by the YPG on Thursday from Syrian Islamist rebels. The YPG controls much of Syria's northern border with Turkey.
Speaking on Turkish TV on Saturday, PM Ahmet 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.
On Sunday, Saleh Muslim, the co-chair of the YPG, told Reuters that jihadists would soon return to the area if Kurdish fighters were driven out.
Turkey's state-run Anadolu Agency said Turkish forces shot at YPG fighters inside Syria on Sunday after coming under fire themselves.
Ankara sees the group as being linked with Kurdish guerrillas from PKK, which has waged a campaign against security forces in Turkey for decades.
In other developments:
Saudi Arabia confirms its jets, which are taking part in sorties against the so-called Islamic State (IS), are now stationed at the Incirlik air base in Turkey
The confirmation comes a day after Turkey's Foreign Minister Mevlut Cavusoglu said troops from his country and Saudi Arabia could participate in a