5 years ago, Syria was world's second-largest refugee host. Now, it's set to be the world's biggest source of refugees

A Syrian woman poses for a photo with her four-year-old son at the Vrazhdebna refugee centre in the Bulgarian capital of Sofia on Oct. 24, 2013.

Syrians fleeing the civil war in their homeland are about to displace Afghans as the world's largest refugee population, the United Nations said Tuesday.

Briefing the General Assembly by video link, UN High Commissioner for Refugees Antonio Guterres painted a devastating picture of the humanitarian crisis as a result of the three-year conflict.

He said nearly 2.5 million Syrians have now registered as refugees with UNHCR in neighboring countries in the Middle East.

"Five years ago Syria was the world's second-largest refugee hosting country. Syrians are now about to replace Afghans as the present biggest refugee population worldwide," he said.

"And it breaks my heart to see this nation that for decades welcomed refugees from other countries ripped apart and forced into exile itself."

Guterres demanded "robust international support" for Syria's neighbors to offset the "enormous cost" that comes with welcoming hundreds, if not thousands, of Syrians every day.

The burden on the tiny population of Lebanon, for example, was the equivalent of France being inundated by nearly 15 million refugees, Russia by 32 million and the United States by 71 million, he said.

He said the World Bank estimates that unemployment in Lebanon may double by the end of the year and that the Syrian crisis could cost it $7.5 billion.

Guterres linked the conflict to a surge of fighting in Iraq's western Anbar province and an increase of violence in Lebanon.

"A further destabilization in the Middle East could have disastrous consequences for the rest of the world," he said.

He called on countries outside the region to allow Syrians to find refuge there and do more to provide them with additional protections such as resettlement and flexible visa arrangements.

"There is something fundamentally wrong in a world where even people fleeing a conflict as horrific as this one are being pushed back from land borders or have to risk their lives at sea, submitting themselves to appalling human rights violations by smugglers and traffickers because they have no other way of reaching territories where they hope to find asylum," he said.

More than five million Afghan refugees fled war, oppression and poverty, mostly for Iran and Pakistan, in the past three decades.

And there are still 2.55 million Afghan refugees, according to the UNHCR website.