Syria has one of the world's largest arsenals of chemical weapons and Washington has been on high alert since last year for any possible use or transfer of chemical weapons by Assad's forces. It feared that an increasingly desperate regime might turn to the stockpiles in a bid to defeat the rebellion or transfer dangerous agents to militant groups such as Lebanon's Hezbollah, which the Syrian government has long supported.
At the time, officials noted movement of some of the Syrian stockpiles but said none appeared to be deployed for imminent use. Still, President Barack Obama declared the use, deployment or transfer of the weapons to be his "red line" for possible military intervention in the Arab country.
Sen. Lindsey Graham, R-S.C., a member of the Armed Services Committee, raised the prospect of deploying U.S. troops to Syria to secure the stockpile of chemical weapons.
"If the choice is to send in troops to secure the weapons sites versus allowing chemical weapons to get into the hands of some of the most violent people in the world, I vote to cut this off before it's a problem," Graham told a group of reporters. "This administration's handling of Syria is going to cause incredible problems in the Mideast and compromise our national security."
But another member of the committee, Sen. Kelly Ayotte, R-N.H., said the United States "should take every step that we can short of boots on the ground."
At a separate congressional hearing, António Guterres, the U.N. high commissioner for refugees, said the international community faces a "tipping point" in Syria, with a fast-moving refugee crisis.
The number of refugees arriving in neighboring countries has jumped to 14,000 in a 24-hour period, up from 3,000 in December, 5,000 in January and 8,000 in February, Guterres said. Lebanon has 360,000 registered Syrians, Jordan more than 350,000 and Turkey some 260,000.
"The refugee crisis has been accelerating since last summer, and has reached staggering proportions since the beginning of this year," Guterres told a Senate Foreign Relations subcommittee. He said the world community needs "to be prepared for things to get worse before they get better."
After Assad falls, Syria could end up like the Balkans, Stavridis told the Armed Services panel.
"We saw in the Balkans 100,000 killed, 1 million people, 2 million people pushed across borders, (and) two significant wars, one in Bosnia, Herzegovina, one in Serbia, Kosovo," Stavridis said. "I think, unfortunately, that's probably the future in Syria. It's going to be after the Assad regime falls. I think, there's going to be every potential for a great deal of revenge killing, interreligious conflict between various segments of the population, and it's very difficult to see the pieces of Syria going back together again very easily."
The violent, unending war has prompted some in Congress to offer legislation and demand greater action by the Obama administration. But a war-weary American public has been slow to embrace many of the efforts.
In the latest proposal, Sens. Bob Casey, D-Pa., and Marco Rubio, R-Fla., offered a bipartisan measure that would provide non-lethal aid to vetted Syrian opposition groups battling the Assad regime, such as body armor and communications equipment.
Casey and Rubio left open the possibility of arming the rebels at a later date.
"Down the road we may make another determination," Casey said when asked about arming the rebels.
Associated Press writer Bradley Klapper contributed to this report.
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