Syria's main opposition National Coalition on Wednesday said any political settlement to the country's conflict must start with the departure of President Bashar al-Assad, implicitly rejecting a US-Russian call for dialogue with the regime.
"The National Coalition welcomes all international efforts which call for a political solution to achieve the aspirations of the Syrian people and their hope for a democratic state, so long as they begin with the departure of Bashar al-Assad and his regime," the umbrella group said.
The response could be a blow to the US-Russian initiative, which is based on a deal agreed in Geneva that makes no mention of Assad stepping down.
The opposition has long insisted that the embattled president cannot stay on as part of any resolution to the conflict.
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But the regime insists that Assad's future will be decided in elections, with a presidential vote scheduled for 2014.
The US-Russia initiative was announced by US Secretary of State John Kerry and his Russia counterpart Sergei Lavrov at a Moscow news conference on Tuesday.
"We agreed that Russia and the United States will encourage both the Syria government and opposition groups to find a political solution," Lavrov said.
He said both nations were ready to use all their resources to bring "the government and opposition to the negotiating table."
Lavrov and Kerry said they hoped they could convene an international conference by the end of May to build on a deal agreed by world powers in Geneva last June for a peaceful solution in Syria.
The Geneva agreement, which was never implemented, set out a path towards a transitional government but without spelling out Assad's fate.