U.S. commanders have laid out a range of possible options for military involvement in Syria, but they have made it clear that any action would likely be either with NATO backing or with a coalition of nations similar to the NATO-led overthrow of Libyan dictator Col. Moammar Gadhafi in 2011.
The White House announced Thursday that intelligence officials have concluded that the regime of Syrian President Bashar Assad has twice used sarin gas on its own people. But even though President Barack Obama has called that a "red line" for taking some kind of further action to assist the rebels, administration officials said Thursday the intelligence wasn't solid enough to warrant such a move.
On Thursday, U.S. officials said that there has been no new movement of U.S. military assets to the region.
The military options could include establishing a no-fly zone or a secured area within Syria, launching airstrikes by drones and fighter jets and sending in tens of thousands of ground forces to secure the regime's chemical weapons caches.
Setting up a no-fly zone over Syria would present a greater challenge than it did in Libya because Syria has a more sophisticated and robust air defense system. Crippling it would require jamming the radars and taking out the missile sites, or possibly even using some type of cyberattack to interfere with the system.
According to a report by the Institute for the Study of War, Syria's largely Soviet-era air defense system includes as many as 300 mobile surface to air missile systems and defense systems, and more than 600 static missile launchers and sites.
Some senators have also pressed for the U.S. to set up a narrow, so-called safe zone inside Syria, along its border with Turkey where citizens could go and be safe. To do so would also require neutralizing Syria's air defenses. The U.S. could use a variety of methods to target key military command locations or attack air defense systems, including bombers, fighter jets from both ships and military bases in the region, missile launches from warships in the Mediterranean Sea and hunter-killer drones, such as those based at Sigonella Naval Air Station in Sicily.
There are currently no U.S. Navy aircraft carriers in the Mediterranean, but fighter jets launched off a carrier in the Red Sea could reach Syria using refueling aircraft if needed.
During a recent Senate Armed Services hearing, Adm. Jim Stavridis, the top U.S. commander in Europe and NATO's supreme allied commander, said there is a "great deal of discussion" among allies about the various options, including the no-fly zone and providing additional lethal support to the rebels.
The U.S. has taken only minimal military steps so far, including the deployment of about 200 troops to Jordan to assist that country's military. The U.S. also participated in NATO's placement of Patriot missile batteries in Turkey near the border to protect against an attack from Syria.
A new Army headquarters unit is being deployed to replace the 200 troops in Jordan, giving the U.S. a stronger command and control unit, if the decision is made to send any additional forces.
In testimony to Congress last week, Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, was asked whether he was confident that U.S. forces could secure the chemical weapons caches within Syria.
"Not as I sit here today, simply because they've been moving it and the number of sites is quite numerous," Dempsey said.