The "Friends of Syria", an alliance of mainly Western and Gulf Arab countries who oppose Syrian President Bashar al-Assad, urged opposition groups on Sunday to attend this month's peace talks, saying there was no other route to a political solution, Reuters reported.
With 10 days to go until the first direct talks between the opposition and President Bashar al-Assad's government - set for January 22 in Switzerland and dubbed "Geneva 2" - Western backers have struggled to unify rebel groups.
The main political opposition body in exile, the Syrian National Coalition (SNC), has been plagued by internal bickering. It postponed a decision on whether to attend until next week after nearly a quarter of its 121 members threatened to resign following after the re-election of its Saudi-backed leader, Ahmad al-Jarba.
In a final statement, the 11 core Friends of Syria nations urged the SNC to attend the talks on the shores of Lake Geneva.
"We invite them to form, as soon as possible, a delegation of opposition forces to participate in the political process," the joint statement said.
"There is no other political solution," French Foreign Minister Laurent Fabius said. "There will be no political solution for Syria unless 'Geneva 2' meets."
Even SNC participation at Geneva 2 is no guarantee that there will be an interlocutor in the talks who can truly represent the armed rebellion.
Led from abroad, the SNC has limited influence over the fighters on the ground who are acceptable to the West, and none over the more radically Islamist rebels who have supplanted them on many fronts of the rebellion.