Western powers have condemned efforts by the Syrian government to set limits to the agenda of fresh peace talks starting on Monday.
Syria's Foreign Minister Walid Muallem on Saturday ruled out any discussion of presidential elections.
US Secretary of State John Kerry responded by accusing Damascus of "trying to disrupt the process".
The UN-led talks represent the first serious diplomatic intervention since Russia began air strikes in September.
At the Geneva talks, diplomats are hoping to build on the fragile and partial truce, which has reduced the level of violence in Syria since it came into effect at the end of February, foreign media reports.
Mr Kerry met foreign ministers from France, Germany and the UK in advance on Sunday.
A cessation of hostilities agreed by most participants in the conflict began late last month. It excludes so-called Islamic State (IS) and al-Qaeda's branch in Syria.
The purpose of the partial and temporary truce was to enable the warring sides and their foreign backers to launch a fresh attempt to end the five-year conflict.