Addressing the "Seventh Annual Ambassadors Conference" in Turkish capital Ankara, Antonio Guterres said: "It is essential to recognize that Turkey has experienced one of the largest refugee influxes in the world of the past few decades."
Turkey has adopted an open-door policy for civilians fleeing from war in its conflict-ridden neighbors, Syria and Iraq.
It has given refuge to at least 1.6 million Syrians since the beginning of the civil war in March 2011, according to UN figures. Ankara also spent more than $5 billion on refugees so far, according to the Turkish Finance Ministry.
"This is to a large extent the result of your generous open door policy in relation to Syrian refugees," Guterres added.
Saying that the international community has largely lost its capacity to prevent and to solve conflicts, Guterres said, "It is important to think what can be done."
"Only with a structured, multipolar world and with strong multilateral institutions, I think it would be possible to mobilize the international community to address the challenges of our time," he said.