The United States says some "kinks" have to be resolved in a pact between Syrian opposition forces if peace talks are to resume next week.
A meeting of Syrian opposition politicians and rebels in Saudi Arabia produced a statement of principles on December 10 to guide proposed UN-backed peace talks with the government of President Bashar al-Assad.
But U.S. Secretary of State John Kerry said on December 11 that there were "some questions and kinks" in the document.
Those must be addressed if a planned high-level diplomatic conference is to be held as scheduled at the United Nations on December 18.
The framework document agreed to by opposition groups says Assad would be allowed to stay in power until a transitional government was formed. They had previously demanded that he leave before any negotiations took place.