U.S. Secretary of State John Kerry says he is confident the Syrian opposition will attend this month's peace talks in Geneva.
Kerry said after a foreign ministers meeting in Paris Sunday that coming to the talks would be a test of credibility for all parties.
The Western-backed Syrian National Coalition has said it will decide by the end of the week whether to attend the January 22 talks.
Opposition leaders have expressed misgivings about sitting at the negotiating table with representatives of Bashar al-Assad's government.
Assad has said the Syrian government will attend the talks, but has said that only the Syrian people can decide the country's future.
French Foreign Minister Laurent Fabius said at the Friends of Syria meeting Sunday that the goal of the talks is setting up a transitional government for Syria "with full executive powers."
Syrian National Coalition president Ahmed Jarba said the Friends of Syria unanimously agree that "Assad and his family have no future in Syria."
The Syrian Observatory for Human Rights says rebel-on-rebel clashes have killed nearly 700 people over the past nine days in northern Syria - the worst infighting among Assad opponents since the country's civil war began in 2011.
Al-Qaida-linked rebels, moderate Islamists and Western-backed rebels have turned against each other in recent weeks.