Syria's opposition on Saturday declared that President Bashar Al-Assad must leave power, dead or alive, if looming peace talks to end five years of civil war are to succeed.
UN-brokered talks are set to begin in Geneva on Monday, in the latest international push to end a conflict that has killed more than 270,000 people and forced half the country from their homes.
"We believe that the transitional period should start with the fall, or death, of Bashar Al-Assad," chief opposition negotiator Mohammad Alloush told the AFP news agency in an interview with another press agency in Geneva.
"It cannot start with the presence of the regime, or the head of this regime still in power," he added.
The United Nations is pushing for a transitional government and a new constitution to be put in place in six months. Legislative and presidential elections would be held next year.
The High Negotiations Committee opposition group has insisted the transitional government be given full executive powers, but the regime dismissed the idea outright ahead of the talks.
"We will not talk with anyone who wants to discuss the presidency… Bashar Al-Assad is a red line," Syrian Foreign Minister Walid Muallem told a Damascus news conference earlier on Saturday.
"If they (the HNC) continue with this approach, there's no reason for them to come to Geneva," he stated.
Muallem also said that the UN's envoy to Syria, Staffan de Mistura, had "no right" to discuss future presidential elections.
"Neither he nor anyone else, whoever they may be, has the right to discuss presidential elections," Muallem insisted, adding, "This right is exclusively for the Syrian people."
The Syrian foreign minister said the negotiations would aim to form a "unity government" which
would then appoint a committee to either write a new constitution or amend the existing one.
"Then we will have a referendum for the Syrian people to decide on it," he said, adding that a federal division of Syria was not an option.
Fighting has eased since a landmark ceasefire between Syria's regime and rebels, bar some Islamist groups, took effect two weeks ago.
But Alloush accused the regime and its ally Russia of not abiding by the truce, which it said had been violated hundreds of times since it began on February 27.
"There have been more than 350 violations during the 14 days and that shows the regime violated the truce, or didn't commit to it," he said.
AFP contributed to this report.