Amin Awad, UNHCR's director for the Middle East and North Africa, said the world was becoming numb to the refugees' needs. "Now when we talk about a million people displaced over two months, or 500,000 overnight, the world is just not responding," he told reporters in Geneva.

The 13.6 million include 7.2 million displaced within Syria - an increase from a long-held U.N. estimate of 6.5 million, as well as 3.3 million Syrian refugees abroad, 1.9 million displaced in Iraq and 190,000 who have left to seek safety.

The vast majority of Syrian refugees have gone to Lebanon, Jordan, Iraq and Turkey, which Awad said "are putting us all to shame" with their support for homeless Syrian families."

“Other countries in the world, especially the Europeans and beyond, should open their borders and share the burden."

UNHCR says it is short of $58.5 million in donations to prepare 990,000 people for winter, money that would cover basic supplies such as plastic sheeting and warm clothing.

Without funds to cover all its needs, the agency is prioritising assistance to people at higher, colder altitudes and then the more vulnerable such as newborn babies.