U.S. Secretary of State John Kerry said there are "kinks" (issues) that must be worked out in the framework agreement reached this week by Syrian rebel groups for peace talks with the government.
Kerry, however, said he is confident those issues will be resolved. He did not elaborate on what needs to be addressed.
He spoke on the sidelines of a U.N. climate conference in Paris.
A vast range of rebel groups agreed to the framework at a two-day meeting in the Saudi capital that ended Thursday, marking a step forward for Syria's badly fragmented opposition.
Proposed peace talks
The framework would guide proposed U.N.-backed peace talks with the government.
More than 100 representatives from Syria’s political and armed factions attended the meeting in Riyadh. The group still must pick its representatives for a negotiating team.
“We know there is still more difficult work to do and not every issue going forward has been resolved,” said State Department spokesman John Kirby.
The talks in Saudi Arabia resulted from a plan agreed to last month by 20 world powers meeting in Vienna. The so-called International Syria Support Group set a January 1 deadline for the start of talks between the Assad government and moderate opposition groups as part of a broader plan for a political transition in Syria.
'No role' for Assad
The Saudi Press Agency said the opposition groups “agreed that the aim of political settlement is to establish a state based on [the] principle of citizenship with no role of Bashar al-Assad in any political arrangements in the future.”
Kerry welcomed the “positive outcome” of the Riyadh meeting.
“We appreciate that this extremely diverse group of Syrians put aside differences in the interest of building a new Syria,” he said in a Thursday statement.
Reports Thursday indicated that one of Syria’s main rebel groups, the Ahrar al-Sham Islamist group, had pulled out of talks. However, Kirby said the group did participate in the negotiations.
Earlier Thursday, on the sidelines of climate talks in Paris, Kerry said plans are under way for a possible ministerial meeting under U.N. auspices in New York next week. The meeting would serve as a follow-up to the Vienna talks.