MONTREUX, Switzerland (REUTERS) - A United Nations envoy was to meet delegations from Syria's government and its foes on Lake Geneva on Thursday, trying to salvage peace talks after an acrimonious start by focusing on local ceasefires and prisoner swaps rather than a political deal.

The first day of the talks on Wednesday was dominated by fierce rhetoric from President Bashar al-Assad's government and its foes. Brought together for the first time in almost three years of war, each accused the other of atrocities and showed no sign of compromise.

Despite the bitterness, officials still 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.

"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," UN envoy Lakhdar Brahimi said.

More than 130,000 people are believed to have been killed, nearly a third of Syria's 22.4 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.

Wednesday's opening ceremony saw global powers vigorously defend their sides, with Western countries, Arab states and Turkey all joining the opposition in demanding a transitional government that would exclude Mr Assad.

Russia, his main global supporter, said the focus of talks should be on fighting "terrorism", a word the Syrian government applies to all of its armed opponents.

In the most dramatic moment of the conference, Assad's foreign minister accused opposition fighters of raping dead women, killing foetuses and eating human organs, drawing a rebuke from UN Secretary-General Ban Ki-moon for using inflammatory language.

Foreign Minister Walid al-Moualem also dismissed any suggestion that Mr Assad might leave power, saying no international forum had the right to question the president's legitimacy.

Western and Arab states declared Mr Assad must go.

The main negotiations, expected to last up to a week, are not due to begin until Friday, giving mediators a day to lower the temperature and focus on pragmatic steps.

UN envoy Brahimi was due to meet the two Syrian delegations separately on Thursday in Montreux, a Lake Geneva resort. Beginning on Friday, the talks will move to the city of Geneva, where Mr Brahimi will shuttle back and forth between the two delegations.