Syria's government and opposition, meeting for the first time, have vented their mutual hostility but a UN mediator said the warring sides may be ready to discuss prisoner swaps, local ceasefires and humanitarian aid.
Russia said on Wednesday that the rival sides had promised to start direct talks despite fears that a standoff over President Bashar al-Assad's fate at the meeting in Switzerland would halt the push for a political solution to Syria's civil war, which has killed more than 130,000 and made millions homeless.
Even if the sides are willing to talk about limited confidence-building measures, expectations for the peace process remain low, with an overall solution to the three-year war still far off.
The US and the Syrian opposition opened the conference by saying that Assad lost his legitimacy when he crushed the once-peaceful protest movement against him and his government.
"We really need to deal with reality," said US Secretary of State John Kerry. "There is no way, no way possible in the imagination, that the man who has led the brutal response to his own people could regain the legitimacy to govern. One man and those who have supported him can no longer hold an entire nation and a region hostage."
The Syrian response was firm and blunt.
"There will be no transfer of power and President Bashar al-Assad is staying," Syrian Information Minister Omran al-Zoabi told reporters.
Western officials were taken aback by the combative tone of Syrian Foreign Minister Walid al-Muallem at the one-day UN peace conference in Montreux, fearing follow-up negotiations would never get off the ground due to the acrimony.
However, international mediator Lakhdar Brahimi signalled that both sides were ready to move beyond rhetoric.
"We have had some fairly clear indications that the parties are willing to discuss issues of access to needy people, the liberation of prisoners and local ceasefires," he told a news conference.
United Nations Secretary-General Ban Ki-moon also told reporters that he had urged the Syrian government to release detainees as a confidence-building measure.
Wednesday's meeting at an hotel in the lakeside city exposed sharply differing views on forcing out Assad both between the government and opposition, and among the foreign powers which fear that the conflict is spilling beyond Syria and encouraging sectarian violence abroad.
Ahmad Jarba, the head of the opposition Syrian National Coalition, accused Assad of Nazi-style war crimes and demanded the Syrian government delegation sign up to an international plan for handing over power.
Muallem insisted Assad would not bow to outside demands, denouncing atrocities committed by rebels supported by Arab and Western states that were present in the room.
Muallem called on foreign powers to stop "supporting terrorism" and to lift sanctions against Damascus.
He insisted Assad's future was not in question, saying: "Nobody in this world has a right to withdraw legitimacy from a president or government other than the Syrians themselves."