Syria's opposition leader has laid out his demands for talks on ending his country's civil war, calling for the creation of a transitional government that does not include President Bashar al-Assad.
Ahmed Jarba, head of the National Coalition of Syrian revolution and opposition forces, said in the Swiss city of Geneva on Thursday that he was looking to a future without Assad.
Russia, Assad's major backer, had given assurances that it was not "holding on" to Assad, he said.
Rival sides in the Syrian conflict were due to begin on Friday several days of main negotiations under the auspices of the UN and major world powers.
The negotiations, expected to last up to a week, will be held at the UN headquarters in Geneva.
The opposing views of Assad's future underline the difficulties facing the Geneva talks - the first time the government and opposition sides have met since the fighting began.
Lakhdar Brahimi, the UN envoy, will meet the two sides in the same room on Friday and explain how he plans to proceed. The heads of delegations will address Brahimi, but not each other.
The talks remain fragile, however, with both sides threatening to pull out.
The government says it will not discuss removing Assad, while the opposition says it will not stay unless Assad's removal is the basis for talks.
In his remarks on Thursday, Jarba said the international community now realised that Assad cannot stay in power.
"We have started to look into the future without him. Assad and all of his regime is in the past now. Nobody should have any doubt that the head of the regime is finished. This regime is dead," Jarba said.
He said the negotiations would be long and difficult, and would look at all the "core issues" as a package deal, including the creation of a transitional governing body.
"This is the basis of our negotiations and we will demand it," he said.
Syria government officials, who left talks with a UN envoy on Thursday evening without making any statement, have insisted that Assad is not going anywhere.
John Kerry, the US secretary of state, also said there was no sign Assad was ready to quit, although he insisted the Syrian leader had no place in his country's future.
"This is a man who has committed war crimes and still somehow wants to claim legitimacy to be able to govern the country," Kerry said in an interview with Al-Arabiya television.
But Kerry said there could be a place for officials from Assad's government in a transitional government as long as they "do not have blood on their hands".
Few expect the peace talks to result in a breakthrough to end the war, since Sunni religious fighters who disdain the Western and Arab-backed opposition are not present at the talks, and nor is Iran, Assad's main regional backer.
Among the many difficulties with the process, the opposition delegation does not include the al-Qaeda-linked Sunni groups who control much of the territory in rebel hands and have denounced those attending the talks as traitors.
Rebel ranks have been divided, with hundreds killed in recent weeks in battles between rival factions and the al-Qaeda-linked Islamic State of Iraq and the Levant.
Ayman al-Zawahiri, al-Qaeda leader, has called on opposition fighters to unite.
|UN envoy to press Syrian rivals on humanitarian issues
But officials hope they can salvage the process by starting with more modest, practical measures to ease the plight of millions of people on the ground, especially in areas cut off from international aid.
More than 130,000 people are believed to have been killed in the fighting, nearly a third of Syria's 22 million people have been driven from their homes, and half are in need of international aid, including hundreds of thousands in areas cut off by fighting.
Against this backdrop, the UN humanitarian chief has urged the Syrian delegations to remember their people and try to reach local ceasefires to allow vital food and medicines to reach millions of civilians in dire needs.
Valerie Amos said on Thursday that Brahimi would press the government and opposition on these humanitarian issues at meetings due to start later in the day.
"Remember your people. Remember that you are all Syrians. You can be talking about your child, your mother, your father of your all family that could be facing this horror. Put the people first," Amos said.
"I have discussed this with Mr Brahimi and he'll continue to push this. Because political negotiations can take a very long time. And as we saw yesterday, there are big differences between the parties."
Amos said it was crucial to gain access to about 250,000 people trapped in besieged communities, many of them in Aleppo, Homs and near Damascus, who have been out of reach for many months.
Another 2.5 million people are in "hard-to-reach" areas, having received UN relief supplies just once or so, she said.
Amos, who submitted a confidential written brief to the UN Security Council last Friday, said that there had been little improvement since world powers called unanimously in October for both sides to grant greater access for aid workers and convoys.