Yildirim -- whose foreign minister, Mevlut Cavusoglu, made a surprise visit to Iran this week -- said Ankara will step up efforts to reduce "instability" in the region.
"We say the bloodshed needs to stop. Babies, children, innocent people should not die. That's why Turkey will be more active in trying to stop the danger getting worse in the next six months, compared with before," Yildirim told foreign reporters in Istanbul.
Yildirim said Syrian President Bashar al-Assad can remain temporarily during a transition period as "he is one of the actors today no matter whether we like it or not".
"We believe that the PKK, Daesh and Assad should not be in the future of Syria," he added, referring to the Syrian Kurds and the Islamic State group in the war-torn country.
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Yildirim said it was "out of the question" for Turkey to talk with the Syrian leader, and said regional countries Turkey and Iran as well as Russia and the United States must work toward a solution in Syria.
"That is our objective. We are not pessimistic. We have even left it late. Therefore, as Turkey, we will work more because the instability there pains us."
After Syrian regime jets pounded US-backed Kurdish forces in northeastern Syria for a second day yesterday, the Turkish premier said Damascus understood that Kurds in northern Syria have become a threat.
"This is a new situation... It is clear that the (Syrian) regime has understood the structure Kurds are trying to form in the north (of Syria) has started to become a threat for Syria too," he added, referring to the Syrian Kurds' bid to join up regions under their control.