Syria peace conference opens, divided over Assad | Reuters

Syria's government and its enemies came face to face on Wednesday for the first time as a peace conference began in Switzerland which world powers hope can at least start a process to end three years of civil war.

There was immediate evidence of sharp differences, as U.S. Secretary of State John Kerry insisted that President Bashar al-Assad must step down, while Russian Foreign Minister Sergei Lavrov cautioned against outsiders meddling in Syria's affairs.

United Nations Secretary-General Ban Ki-moon opened what will be a day of speeches at Montreux on Lake Geneva from more than 40 delegations, including the opposing sides in Syria, by painting a bleak picture of the suffering of millions and of abuses of human rights by all the warring parties.

"Syrians must start talking to each other again," Ban said, urging both sides to reach a comprehensive settlement based on the U.N. Geneva Communique, under which world powers called in 2012 for a transitional government to oversee change in Syria.

"There is no alternative to ending the violence ... I appeal to all of you to show greater vision for humanity."

Calling the challenges ahead great but not insurmountable, he called for immediate access for aid to areas under siege.

Western powers and Russia have sought to set aside their own sharp differences over whether Assad must be forced to make way for an interim administration and have backed the conference as a way to stop the spread of communal and sectarian violence spreading across the region.