AMMAN - The Syrian opposition feels badly let down by Washington's decision to do a deal with Moscow to eliminate Bashar al-Assad's chemical weapons but diplomats are warning the Syrian National Coalition that it risks losing Western support if it cannot adapt to new realities.
The rift that has alienated the Syrian opposition from the United States threatens to derail international efforts to end the two and a half year civil war, diplomatic and opposition sources said.
It comes as the war has turned into a something of a stalemate on the battlefield and the rebels had been looking to the United States to tilt the balance in their favour by intervening militarily to punish Assad for using chemical weapons.
The behind the scenes dispute, in which Saudi Arabia and Turkey appear to be siding with the opposition, developed last week as the United States and Russia made their deal to destroy Assad's chemical arsenal following a nerve gas attack on rebel areas of Damascus that killed hundreds, the sources said.
The agreement, from which the United States hopes a wider political settlement can emerge, has reduced the likelihood of a US strike on Assad's forces that the opposition had hoped would weaken him militarily and force him to attend a planned new peace conference.
The opposition is therefore furious that Washington suddenly and without its knowledge changed course a week after informing leaders of the main Syrian National Coalition that a strike was imminent, according to coalition members.
In the opposition's view, the deal with Russia contains a de facto admission of the legitimacy of the Assad government, undermining the goal of Syrian uprising and the likelihood that any peace talks will result in Assad's removal.
US President Barack Obama said this week that while it was still his goal to "transition" Assad out of power, dealing with his chemical weapons would come first.
Diplomats who monitored a major opposition meeting in Istanbul at the weekend said a lack of flexibility by the coalition in the way it deals with the changing diplomatic priorities, as spelled out by Obama, could rob the opposition of Western support.
The Arab- and Western-backed Free Syrian Army needs what friends it can get as it struggles to deal with mounting chaos in rebel areas.
Al Qaeda-linked groups, ostensibly opposed to the Assad government, are also fighting against the mainstream Syrian rebels and have even defeated FSA units.
The worsening outlook for the opposition, and the rift with Washington, became clear at its meeting in Istanbul, when US diplomats did not show up.
Western diplomats who were there criticised the opposition's clumsily negative reaction to the chemical weapons deal, which has been largely supported by the international community.
"The coalition just has to make the right noises and realise that there is a big powers game going on," one diplomat said.
"They cannot ignore that the removal of Assad's chemical weapons is a good thing and the people in Ghouta are probably sleeping better now," the diplomat said, referring to the site of the August 21 chemical attack.
"Otherwise our parliaments will not keep giving us the mandate to support the Syrian opposition forever. We're already having to convince lawmakers that not every other Syrian is an al Qaeda member."