(CNN) — With Thursday’s news that U.S. intelligence shows evidence that sarin gas has been used in Syria, all eyes are now on President Obama, who said in August that any sign of chemical weapons use in the country’s civil war would be “a red line for us.”
Here’s a look at the current situation and how that might change should the U.S. military be ordered to act.
The Obama administration said Thursday that it is working to gather more information on the reports of sarin-gas use and is calling for a full-scale U.N. investigation into what may have happened.
“Given the stakes involved, and what we have learned from our own recent experience, intelligence assessments alone are not sufficient — only credible and corroborated facts that provide us with some degree of certainty will guide our decision-making,” said a White House letter to lawmakers.
What role is the U.S. currently playing in the Syrian civil war?
The first direct U.S. support for the armed opposition arrived in the country last month in the form of food and medicine.
Obama signed off on a new package of non-lethal aid this month. The aid is expected to include body armor, night-vision goggles and other military equipment.
And last week, Defense Secretary Chuck Hagel ordered the deployment of up to 200 additional U.S. troops to Jordan.
The troops — essentially military planners — will work alongside Jordanian forces to “improve readiness and prepare for a number of scenarios.”
The new deployment of troops, who are from the headquarters of the 1st Armored Division at Fort Bliss, Texas, will include communications and intelligence specialists who will assist the Jordanians and “be ready for military action” if Obama were to order it, a Defense Department official said.
There have been several dozen American troops, mainly Special Forces, in Jordan for the past year, assisting the Jordanians.
But that group has been very ad hoc, the defense official said. This new deployment makes the U.S. military presence more official and is the first formalized ongoing presence of an American military unit in Jordan in recent years.
Would NATO join the U.S. in a military intervention?
Questions still remain about whether NATO would assist the U.S. militarily, similar to its help in enforcing a no-fly zone over Libya during that country’s period of civil unrest.
NATO has flatly ruled out military intervention.
But NATO Secretary General Anders Fogh Rasmussen noted Tuesday that “the situation in Syria has dramatically deteriorated” and “continues to pose a threat to regional stability.”
He said the alliance is “extremely concerned about the use of ballistic missiles in Syria and the possible use of chemical weapons.”
He said NATO has not been asked to intervene but suggested that it could be drawn further into the crisis to address spillover into its backyard.
“There is no call for NATO to play a role, but if these challenges remain unaddressed, they could directly affect our own security,” he said. “So we will continue to remain extremely vigilant.”
What military options are under consideration?
NATO officials and Washington have looked at options including:
• Targeting Syria’s air defenses: NATO has installed Patriot missile batteries in Turkey, near its border with Syria, which could be aimed to shoot down Syrian aircraft, NATO commander Adm. James Stavridis said last month.
But Turkey allowed the missile batteries to be placed there only for defensive purposes, and NATO nations would have to agree before they could be used for offensive strikes against Syria.
That’s not something under immediate consideration, Stavridis has said.
• Airstrikes: The U.S. military has enough airpower in the region to take action against Syria, according to officials. That includes fighter jets and bombers spread out across air bases in the Middle East and nearby aircraft carriers. The U.S. Navy also has warships equipped with Tomahawk missiles, which could be used to hit chemical weapons supplies.
But such strikes pose a danger of releasing chemical agents into the air around civilian populations in Syria, U.S. officials told CNN last month.
Other options include bombing runways to prevent Syrian aircraft from taking off or disrupting communication between the regime leaders and ground commanders.
• Ground troops: The United States has no plans to put “boots on the ground” in Syria. But the Pentagon is a planning machine, so the Defense Department last year came up with a military analysis of a ground option should the president request it.
According to the analysis, it would take up to 75,000 troops to secure Syria’s chemical weapons facilities if they were in danger of being looted. An actual deployment would probably involve far fewer ground troops, and from various nations, but it underscores the scope of the challenge.
Before ground troops would go in, weeks of airstrikes would be needed to destroy Syria’s air defenses.
What are the pitfalls of military involvement?
Hagel cautioned lawmakers on the Senate Armed Services Committee last week about the difficulties surrounding any direct U.S. military action in Syria.
“It could embroil the United States in a significant, lengthy and uncertain military commitment,” he said.
He called military intervention “an option but an option of last resort.”
Joint Chiefs Chairman Gen. Martin Dempsey said the United States could send troops to Syria if the regime of President Bashar al-Assad fell to rebels, if needed, to secure the country’s chemical weapons cache.
But when asked whether he was confident the United States could secure them, Dempsey said, “Not as I sit here today, simply because they have been moving it, and the number of sites is quite numerous.”
Depending on what the administration might decide to do, military intervention also could meet with resistance from a public weary of war after the long conflicts in Iraq and Afghanistan.
CNN’s Barbara Starr, Chris Lawrence and Elise Labott contributed to this report.