The countries that have taken in the refugees say the number could be far higher than three million. Photo taken from BBC
More than three million Syrians are now registered as refugees and the desperate crisis is only getting worse, the UN's refugee agency says.
The UNHCR says Syria is now "the biggest humanitarian emergency of our era" with almost half of all Syrians forced to flee their homes.
The majority of refugees have fled to countries neighbouring Syria, with 1.14 million now seeking shelter in Lebanon.
More than 190,000 have been killed in Syria's three-year civil war.
Opposition groups in Syria have been fighting forces loyal to President Bashar al-Assad since his government suppressed protests against his rule in March 2011.
The situation has been worsened in recent months by the formation and advance of the Islamic State group, who now controls large swathes of Syria and Iraq.
Aysha, 5, stands outside an abandoned building in Istanbul, Turkey, that has been her home for half a year. Photo taken from BBC
'Exhausted and scared'
The UNHCR says one in every eight Syrians has fled across the border and a further 6.5 million are displaced within Syria - half of them children.
Families arriving at refugee camps in neighbouring countries are exhausted and scared, with some having spent a year or more fleeing from village to village inside Syria.
The UN agency says the journey out of Syria is also becoming tougher, with many people forced to pay bribes to armed gangs.
Where Syrian refugees are
1,175,504 in Lebanon
832,508 in Turkey
613,252 in Jordan
215,369 in Iraq
139,090 in Egypt
23,367 in North Africa
6.5 million others are displaced within Syria
In addition to the registered refugees, Syria's neighbours estimate that hundreds of thousands more Syrians have sought sanctuary in their countries - causing enormous strain.
"The Syrian crisis has become the biggest humanitarian emergency of our era, yet the world is failing to meet the needs of refugees and the countries hosting them," said Antonio Guterres, the UN High Commissioner for Refugees.
"The response to the Syrian crisis has been generous, but the bitter truth is that it falls far short of what's needed."
'Violence at a new level'
On Thursday, French President Francois Hollande voiced his regret that the West had failed "to find a solution for the situation in Syria," saying the consequences were clear to all.
"Bashar al-Assad's regime continues without restraint its policy of repression. Refugees continue to gather, their numbers increasing every day, in the neighbouring countries. And terrorist groups are winning more territory - that's the result," he said.
The UN's deputy humanitarian chief, Kyung-wha Kang, said Islamic State was taking violence against civilians in Syria "to a new level" and threatening aid operations in the country.
But US President Barack Obama insisted Thursday that the West would not contemplate working with President Assad against the extremist group.
"I don't think there's a situation where we have to choose between Assad or the kinds of people who carry on the incredible violence that we've been seeing there," he told reporters at the White House.