AMMAN - Rivalry between Qatar and Saudi Arabia has fuelled wrangling within the Syrian opposition that threatens to prevent a united rebel delegation attending international peace talks next week.

Sources in the Syrian National Coalition and diplomats from foreign powers backing the rebels said it remains unclear whether those divisions can be overcome by Friday, when the 120-member Coalition is expected to vote on whether to take part in the conference in Switzerland, known as Geneva-2.

However, some expect that Qatar, which has raised its profile in diplomacy by being quick to back the Arab Spring revolts, will not in the end risk angering Riyadh, Turkey and Western states by having Doha's allies on the Coalition force a boycott of talks that are supported by the other powers.

Earlier this month, 44 members, mostly with links to Qatar, walked out of a Coalition meeting to underline their rejection of attending talks without assurances that key demands would be met. They were also angered by the re-election of Ahmad Jarba, a Saudi-backed Syrian tribal figure, as head of the Coalition.

Diplomats said Qatar's role, which includes supporting some militant Islamist brigades in Syria, had been discussed at a meeting in Paris on Sunday of the Friends of Syria, a group supporting the opposition, which was attended by US Secretary of State John Kerry and other Western foreign ministers.

"The message was that everyone needed to be on a new page in support of Geneva and stop backing militants," a person who was at the meeting said. "There were strong hints that the onus falls on Qatar for a Coalition decision to go to the talks."

Qatar's foreign minister insisted in Paris that the Gulf emirate was not backing one opposition faction over another.

Few members of the Coalition, a body comprised largely of exiled political leaders, are enthusiastic about the meeting, organised by international powers anxious to end the conflict which has destabilised the Middle East for three years.

Coalition members see little prospect of President Bashar al-Assad's delegates making big concessions, let along agreeing to their demand of a transitional administration that excludes Assad from power. As a result, they fear attendance could further undermine their legitimacy within a Syrian opposition that is increasingly dominated by rebel fighters on the ground.

However, a failure to show up next Wednesday would dismay most of the opposition's foreign backers. They might scale back their support for a body that has failed to prevent much of the rebel force in Syria becoming dominated by Islamist militants.

"The Coalition is being asked to go to Geneva without a hint that the talks will result in anything even to save face before the Syrian people," said Nasr al-Hariri, spokesman for the 44 members who walked out this month. "The only way for the Coalition to function as a coalition is by expanding it to restore balance and find a consensus president."

Even those close to Saudi-backed Coalition chief Jarba say they are reluctant to go to Switzerland without some assurance of winning concessions, such as the release of prisoners or the lifting of sieges around rebel-held suburbs of Damascus.

The National Coordination Body (NCB), a coalition rival comprised of centrist politicians who include some members still living in Damascus and tolerated by Assad, said in a statement on Wednesday that it will not attend the peace talks.

The group cited what it described as failure of Russia "to make any worthwhile effort" to pressure the Syrian authorities to take conciliatory steps and lack of U.S. efforts to form a "balanced and convincing" opposition delegation.

Russia, which has shielded Assad from rebel and Western insistence that he step aside, and the United States have discussed such demands as co-sponsors of Geneva-2 but it is unclear that Assad is ready to offer such concessions.