Syria's neighbours, wary of stirring a conflict that could spill back over their borders, would be reluctant partners in a US-led intervention but are ultimately likely to support limited military action if widespread use of chemical weapons is proven.
The White House disclosed US intelligence on Thursday that Syria had likely used chemical weapons, a move President Barack Obama had said could trigger unspecified consequences, widely interpreted to include possible US military action.
Syrian neighbours Jordan and Turkey, their support key in any such intervention, have long been vocal critics of Bashar al-Assad. Prime Minister Tayyip Erdogan, an erstwhile ally of the Syrian President, was among the first to call openly for his overthrow while allowing armed opponents to use Turkish soil.
But their rhetoric has been tempered by the changing circumstances of a war that has dragged on beyond their expectations and grown increasingly sectarian, as well as by the suspicion they will be left bearing the consequences of any action orchestrated by Western powers thousands of miles away.
For Turkey's leaders, facing elections next year, talk of chemical weapons is an uncomfortable reminder of the wave of anti-US sentiment which followed the 2003 US-led invasion of Iraq, justified by intelligence on nuclear, chemical and biological weapons that turned out to be erroneous.
Turkey, which shares a 900-km border with Syria, has reacted cautiously to the US disclosure while Jordan, fearful of the growing influence of radical Islamists in the Syrian rebel ranks, has voiced its preference for a political solution.
"The international community, and especially the peoples of the Middle East, have lost confidence in any report which argues that there are weapons of mass destruction or chemical weapons," said one source close to the Turkish government.
"Right now, no-one wants to believe them. And if Assad uses chemical weapons some day I still think Turkey's primary reaction would be asking for more support to the opposition rather than an intervention."
Turkey's rhetoric on Syria, at least in public, has toned down markedly over the past six months, even as shelling and gunfire spilled over the border and the influx of refugees to camps on its territory swelled to a quarter of a million.
Foreign Minister Ahmet Davutoglu's push for a foreign-protected "safe zone" inside Syria gained little traction among allies and appears to have quietly slipped from the agenda. Even Erdogan, whose speeches were regularly laced with bellicose anti-Assad rhetoric, mentions the conflict less frequently.
But many analysts believe both the pro-US monarchy in Jordan and Erdogan's government in Ankara would toe the line should Washington seek their Co-operation in military action.
Turkey's relations with Washington have at times been prickly - notably in 2003 when it failed to allow the deployment of US forces to Turkey to open a northern front in the Iraq war - but strategic Co-operation has generally remained strong.
Turkish support and bases proved vital, for example, to US forces in Afghanistan, while Turkey hosts a US-operated NATO radar system to protect against any regional threat from Iran.
"Given the texture of the current government's relations with the US and given the history of its discourse on Syria, I think it would be not impossible but rather difficult for Mr Erdogan not to oblige US demands," said Faruk Logoglu, former Turkish ambassador to Washington and vice chairman of the main opposition Republican People's Party.
Although Obama has warned Syria that using chemical weapons against its own people would cross a "red line", he has also made clear he is in no rush to intervene on the basis of evidence he said was still preliminary.
Syria denies using chemical weapons in the two-year-old conflict in which more than 70,000 people have been killed.
Mindful of the lessons of the start of the Iraq war, aides have insisted Obama will need all the facts before deciding what steps to take. But acknowledgement of the intelligence assessment appears to have moved the United States closer - at least rhetorically - to some sort of action, military or otherwise.
Turkey and Jordan would be key to any such move, but they may prove reluctant.
From the outset, Turkey has felt slighted.
Before the crisis, Erdogan cultivated a friendship with Assad, personal ties which he tried to use after the start of the uprising in March 2011 to persuade the Syrian leader to embrace reform and open dialogue. He was rebuffed.
When his strategy changed, he began calling for Assad's removal and allowing the Syrian opposition to organise on Turkish soil. Ankara felt it gained praise from Washington and its allies but little in the way of concrete support.