The US has dismissed a Syrian plan to hold a presidential election on 3 June as a "parody of democracy".
UN chief Ban Ki-moon also condemned the plan, saying it could torpedo efforts to broker a deal to end the three-year civil war, which has killed 150,000.
Government forces have made gains recently, but rebels still control vast territories. It is unlikely that voting would be held in those areas.
President Bashar al-Assad is expected to seek a third seven-year term.