"If anyone thinks we are going to Geneva 2 to hand the keys to Damascus over (to the opposition), then he might as well not go," Information Minister Omran al-Zohbi said in remarks carried by the official SANA news agency.
"The decision rests with President Assad. He will lead the period of transition, if there is one. He is the leader of Syria... And he will remain the president of Syria."
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Zohbi also said that Saudi Arabia, a strong backer of the rebels, should be excluded from the peace conference.
The rebels battling Assad's regime in a war that has claimed 126,000 lives since March 2011 have insisted he step down as part of any transition.
The two sides are set to meet in Geneva on January 22 in talks brokered by the UN-Arab league envoy Lakhdar Brahimi.
But the dispute over Assad's role in the transition, and the endemic divisions among both the external opposition and rebels battling on the ground, have cast doubt over whether the two sides can even reach an agreement let alone implement it.
The National Coalition, an umbrella opposition group, has demanded the creation of a "transitional governing body" with "full executive powers" that excludes Assad and his inner circle.
The conflict began nearly three years ago with peaceful pro-democracy protests inspired by the Arab Spring but escalated into a full-scale civil war after Assad's regime launched a brutal crackdown.
Today hundreds of armed groups, including powerful jihadist brigades affiliated with Al-Qaeda, are battling both the regime and each other, complicating any efforts to reach a political settlement.