By Holly Watt, Zaatari, David Blair in Beirut and Ruth Sherlock in Shatila 03 Sep 2013
The number of Syrian refugees in neighbouring countries has reached two million, while a further 4.3 million people have been displaced within the nation's borders. The fighting has been so intense that the number of refugees has increased almost tenfold in a single year, according to the UN.
"Syria has become the great tragedy of this century - a disgraceful humanitarian calamity with suffering and displacement unparalleled in recent history," said Antonio Guterres, head of the UN High Commission for Refugees, which released the figures.
The milestone of two million refugees was reached as Bashar al-Assad, the Syrian president, challenged the West to provide "the slightest proof" he had used chemical weapons against his people, warning in an interview that any military intervention could spark a "regional war."
According to the UNHCR, the UN's refugee agency, there is no sign of the "tragic outflow" of refugees from Syria ending. One year ago today, the UN said the number of Syrians registered as refugees stood at 230,000 - meaning the total has jumped by almost 1.8 million in the last 12 months. Around 5,000 refugees now flee Syria every day. Of the 2 million to have fled so far, more than half are children aged under 17. The UN said more Syrians were now forcibly displaced than in any other country.
Mr Guterres said the "only solace" was the humanity shown by neighbouring countries, such as Jordan, Lebanon and Turkey, in welcoming the refugees, despite the "overwhelming" burden placed upon them.
The inflow is placing a huge strain on Jordan, which now hosts 515,000 registered Syrian refugees, representing eight per cent of its population of 6.2 million. The equivalent for Britain would be the arrival of 5 million people. Jordan is trying to limit the influx by closing its border, but Syrians manage to slip across by walking long distances.
If Jordan is struggling to contain the inflow, the situation in Lebanon is far more serious. The country hosts more Syrians than any other: 716,000 registered refugees and perhaps another 300,000 undocumented arrivals. Lebanon's population of only four million has grown by a quarter in two years. The equivalent in Britain would be for the population to jump by 16 million.
And the numbers keep rising: unlike Jordan, Lebanon has kept its border open allowing some 8,000 refugees to cross every day.
In Lebanon's capital, Beirut, Syrians have settled in already overcrowded Palestinian refugee camps. About 2,000 families have moved to Shatila camp on the city's southern fringe. When Syria's civil war began, many Lebanese families opened their doors to refugees. But the inflow has been so huge that relations between the new arrivals and host population have become strained.
UNHCR Special Envoy Angelina Jolie said: "The world risks being dangerously complacent about the Syrian humanitarian disaster. The tide of human suffering unleashed by the conflict has catastrophic implications. If the situation continues to deteriorate at this rate, the number of refugees will only grow, and some neighbouring countries could be brought to the point of collapse."