The Syrian President, Bashar al-Assad, says he has no intention of giving up power and will not even discuss it.
Mr al-Assad has been quoted by a Russian news agency as telling visiting Russian MPs that if his government wanted to give up, it would have done so at the very beginning of the country's three-year crisis.
The comments underscored differences between participants as they prepare for talks in Montreux, Switzerland, which are being seen as the most serious global effort yet to end Syria's civil war.
Opposition groups have previously demanded the removal of Mr Assad as a condition of any discussions on a possible transitional government. But the BBC says the Syrian National Coalition, the exiled opposition body, announced on Saturday that it would attend the talks.
More than 100,000 have been killed and millions displaced in Syria's ongoing conflict, and the United Nations hopes the talks will edge the country closer to political transition.