Explainer: Military intervention in Syria

Why is the United States contemplating military action in Syria?

Although the U.S. has refrained from intervening in the war between the security forces of the President Bashar al-Assad's regime and anti-government rebels, President Obama warned a year ago that the U.S. would intervene if "we start seeing a whole bunch of chemical weapons moving around or being utilized." He called this his "red line."

The suspected chemical weapon attack that left hundreds of civilians dead on Aug. 21, 2013, appears to have triggered that red line, with Obama declaring in an interview  that he was "certain" that regime forces were responsible for the incident, which required "international consequences."

What type of military action is being contemplated?

Obama has made it clear that he is not interested in getting "drawn into a long conflict" in Syria, and that he is simply weighing a demonstrative military action -- he called it a "shot across the bow" -- to warn Assad against further use of chemical weapons. Analysts expect that would largely take the form of cruise-missile and possibly air strikes at regime military targets, for a limited period. 

Why is the United States loath to intervene more aggressively to topple the Assad regime?

Unlike in Libya where the  goal of Western intervention was to bring down the Gaddafi regime, the Obama administration is has made clear that it's goal is not to use military force to help bring down Assad, but simply to deter it from using chemical weapons.   "It is not our policy to respond to this transgression with regime change," White House Press Secretary Jay Carney told reporters Tuesday. "That is not what we are contemplating here."

The administration is mindful that the Assad regime has survived because it has a substantial support base, and fears being drawn in to manage an open-ended sectarian civil war. Washington is also concerned that many of the rebels' most effective fighting units are composed of elements hostile to U.S. interestes in the region, particularly the al-Qaeda affiliated Jabhat al-Nusra which Washington has listed as an "international terrorist organization". 

Under whose auspices and on what legal basis could military action be justified?

Russian and Chinese veto power makes U.N. Security Council authorization for any military intervention highly unlikely. The Obama administration would instead have to rely on a "coalition of the willing" to act outside U.N. mandate. Allies such as Britain, France and some key Arab countries have pressed for action, although Prime Minister David Cameron suffered a setback Thursday when his parliament ruled Britain out of participating in military action in Syria.

President Obama is also consulting with congressional leaders to win support for action in Syria. 

What is the purpose of the U.N. inspection?

The U.N. inspectors are searching for evidence that chemical weapons were used in the attack in Ghouta that killed hundreds of civilians. But the inspectors are not tasked with determining who might have used such weapons, simply whether there's forensic evidence that chemical weapons were used. 

Which international players support invention, and which oppose it?

Britain's government has been a strong advocate for action in Syria, but has now been ruled out of participating by the vote of its parliament.

France supports intervention, but only after U.N. inspectors have concluded their investigation.

Russia and China have consistently opposed U.N. Security Council action on Syria, and have warned against any military strike. 

Iran, Assad's greatest ally, has also warned against any military strikes on Syria. 

Turkey, which shares a 560-mile border with Syria, supports military intervention.

Though the Arab League blamed Assad's regime for using chemical weapons to attack civilians, the regional bloc rejected support for military intervention without approval from U.N. Security Council.

Palestinian governments led by Hamas in Gaza and the Palestinian Authority in the West Bank both oppose military strikes on Syria, as have the governments of Lebanon and Iraq. Lebaonon's Hezbollah movement has already intervened militarily in Syria in support of Assad. 

In an attempt to avoid friction with its embattled neighbor, Jordan's Information Minister Mohammad Momani said his country "will not be a launching pad for any military action against Syria."

Al Jazeera and wire services