French Foreign Minister Laurent Fabius said the moderate opposition to the Syrian regime is in "serious difficulty" and that long-delayed peace talks aimed at ending the crisis are in trouble.
"On Syria, I'm unfortunately rather pessimistic," Fabius said.
"The moderate opposition that we support is in serious difficulty," he added, voicing misgivings over the prospects of peace talks known as "Geneva 2", which mediators have been trying to organise to negotiate an end to the conflict.
The talks are scheduled for January 22 in the Swiss city, but Fabius said there were doubts over whether they would make progress towards ending the civil war that has now raged for more than two and a half years and killed more than 126,000 people.
"My fellow European ministers and I are working to make (the talks) a success, but there's room for lots of doubts. And, unfortunately, if this meeting's not a success, it means this martyred country is going to keep suffering -- and neighbouring countries, too," he said.
Fabius was speaking in Monaco as he left the World Policy Conference, a meeting of political and business leaders.
The Free Syrian Army, the moderate rebel group supported by Western powers including France, has been losing ground to Islamist fighters as the insurgency against President Bashar al-Assad has turned into a more complex conflict with schisms between the various rebel groups.
In the latest blow to the Free Syrian Army, the United States and Britain on Wednesday suspended all non-lethal aid to the group after a powerful new rebel alliance, the Islamic Front, seized a Turkish border crossing and nearby weapons warehouses from them.
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Also at the meeting, influential Saudi Prince Turki al-Faisal was equally pessimistic about the prospects for peace in Syria, hitting out at a lack of support for the Free Syrian Army from Washington and London.
"The fighting is going to continue, the killing is going to continue," Turki told journalists.
He criticised a "lopsided" situation in which Assad had access to weapons such as tanks and missiles.
"You name it, he is getting it and the other side is screaming out to get defensive weapons against these lethal weapons that Assad has. Why should he stop the killing?," he said.
"Since the beginning of this conflict, since the FSA arose as a response to Assad's attacks on his people, Britain and the US did not come forward and provide the necessary aid to the FSA to allow it to defend itself."
The prince said a more level playing field would make a ceasefire more likely.
"The Free Syrian Army hasn't been overrun by other opposition groups. The FSA is alive and well in Damascus, Aleppo, Hama, Homs, Deir Ezzor.... Nonetheless, I describe Syria as a festering wound that attracts all the worst bacteria."
The opposition wants the Geneva peace conference to unseat Assad, but his regime has refused to accept any preconditions on the talks.