Along with more than four million people displaced inside Syria, this means more than six million Syrians have been uprooted, out of an estimated population of 23 million.
Antonio Guterres, the head of the Office for the U.N. High Commissioner for Refugees, said Syria is hemorrhaging an average of almost 5,000 citizens a day across its borders, many of them with little more than the clothes they are wearing. Nearly 1.8 million refugees have fled in the past 12 months alone, he said.
The agency's special envoy, actress Angelina Jolie, said "some neighboring countries could be brought to the point of collapse" if the situation keeps deteriorating at its current pace. Most Syrian refugees have fled to Jordan, Lebanon and Turkey.
Despite the grim toll, Assad has not shown any signs of backing down.
Assad and some in his inner circle are from Syria's minority Alawites, or followers of an offshoot of Shiite Islam, who believe they would not have a place in Syria if the rebels win. Most of those trying to topple Assad are Sunni Muslims, with Islamic militants, including those linked to the al-Qaida terror network, increasingly dominant among the rebels.
The missile test came at a time of heightened tensions as Washington weighs sea-launched strikes against Syria. Israel has been increasingly concerned that it could be drawn into Syria's brutal civil war.
Since the weekend, the Obama administration has been lobbying for congressional support for military action against the Assad regime.
The administration says it has evidence that Assad's forces launched attacks with chemical weapons on rebel-held suburbs of the Syrian capital of Damascus on Aug. 21. The U.S. has alleged that the nerve agent sarin was used and that at least 1,429 people were killed, including more than 400 children.
Last week, President Barack Obama appeared poised to authorize military strikes, but unexpectedly stepped back over the weekend to first seek approval from Congress, which returns from summer recess next week.
On Monday, the U.S. administration won backing from French intelligence and reportedly also from Germany's spy agency for its claim that Assad's forces were responsible for the suspected chemical weapons attacks.
The Assad regime has denied using chemical weapons, blaming rebels instead. Neither the U.S. nor Syria and its allies have presented conclusive proof in public.