More than two million Syrians have now fled their country, the UNHCR said Tuesday, as top US officials pressed a robust bid to secure Congress' support for military strikes against the Damascus regime.
The UN refugee agency's grim statistics come as Syrian President Bashar Al-Assad warned that Western military action against him risked igniting a regional war and bringing chaos across the Middle East.
The UNHCR, in a statement released in Geneva, lamented that the number of Syrian refugees had increased nearly 10-fold from a year ago.
"Syria is haemorrhaging women, children and men who cross borders often with little more than the clothes on their backs," the statement said, pointing out that on 3 September, 2012, it had registered just 230,671 Syrian refugees.
In addition to the two million Syrians living as refugees, some 4.25 million people have been displaced within the devastated country since the conflict began in March 2011, according to UN figures.
"Syria has become the great tragedy of this century," UN High Commissioner for Refugees Antonio Guterres said in a statement, describing the situation in the country as "a disgraceful humanitarian calamity with suffering and displacement unparallelled in recent history."
Correspondents and witnesses have reported an even greater exodus of Syrians into neighbouring countries since US President Barack Obama warned last week he was ready to launch military strikes on Assad's regime over its alleged use of chemical weapons.
Obama shocked Washington and the world on Saturday when he decided to seek support for military action in Syria from Congress, putting his plans on hold and effectively giving more time for civilians to leave the country.
As part of White House strategy to persuade sceptical lawmakers to back what Obama said would be "limited" and "narrow" action in Syria, the US secretaries of state and defence were to go before a Senate panel on Tuesday.
In what will be one of the most high-profile political set pieces in Washington in weeks, John Kerry and Chuck Hagel will testify to the Senate Foreign Relations committee.
Kerry will argue that failing to act in Syria "unravels the deterrent impact of the international norm against chemical weapons use," a senior State Department official said on condition of anonymity.
Inaction also "endangers our friends and our partners along Syria's borders... and risks emboldening Assad and his key allies - Hezbollah and Iran," the official warned.
France, which backs Obama in his determination to launch a military intervention in Syria, on Monday released an intelligence report which said Assad's forces carried out a "massive" chemical attack last month.
Based on military and foreign intelligence services, the report said the regime launched an attack "combining conventional means with the massive use of chemical agents" on rebel-held areas around the capital Damascus on August 21.
It said that based on videos, French intelligence had counted at least 281 dead but that reports of up to 1,500 killed were consistent with such heavy use of chemical weapons.
"The attack on August 21 could only have been ordered and carried out by the regime," the report said.
Assad, in a rare interview with Western media released Monday, warned that Western military strikes risked setting off a wider conflict in the Middle East.
"We cannot only talk about a Syrian response, but what could happen after the first strike," Assad said.
"Everyone will lose control of the situation once the powder keg explodes. Chaos and extremism will spread. There is a risk of regional war."
He said France should consider the consequences of taking part in military action.
"There will be repercussions, negative ones of course, on the interests of France," Assad said.
France has emerged as the main US ally in the Syria crisis after the British parliament rejected involvement in any military action.
It was unclear who else may be persuaded to take part in Western action, but NATO chief Anders Fogh Rasmussen said Monday he was personally convinced the chemical attack had taken place and that Assad's regime was responsible.
Rasmussen called for a response that would "send a very clear message" against the use of chemical weapons, but said any military action should be "very short, sharp (and) tailored".
Efforts to win UN backing for military action have been stymied by Russia, which said Monday it remained totally unconvinced that the regime carried out the attack.
Foreign Minister Sergei Lavrov warned that Western military action would sink joint efforts by Washington and Moscow to organise a peace conference in Geneva.
China, which in the past has joined Russia in blocking UN Security Council resolutions against Assad, also said it was "gravely concerned" about the prospect of "unilateral military actions" against Syria.
Fighting continued to rage in Syria meanwhile, with the Syrian Observatory for Human Rights watchdog saying that nearly 90 rebels were killed near Damascus in the previous 48 hours.