Syria's government and opposition, meeting face to face for the first time at a United Nations peace conference, angrily spelled out their hostility on Wednesday as world powers also restated contrasting views on the future of President Bashar Assad.
Opposition leader Ahmed Jarba accused Assad of war crimes that recalled Nazi Germany and demanded that the Syrian government delegation at the one-day meeting in Switzerland immediately sign up to an international plan for a transition of power.
Syrian Foreign Minister Walid al-Moualem insisted Assad would not bow to outside demands and painted a graphic picture of "terrorist" rebel atrocities supported by Arab and Western states who back the opposition and were present in the room.
The U.S. and Russia, co-sponsors of the conference which UN officials hope can launch further negotiations at Geneva, also revealed their differences over Assad in speeches that began what would be a day of formal presentations.
UN Secretary-General Ban Ki-moon, who exchanged sharp words with Moualem when the Syrian minister spoke for more than three times the 10-minute limit Ban had set, opened proceedings at Montreux on Lake Geneva by calling for immediate access to humanitarian aid for 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.
Moscow and Washington differ, however, over whether the 2012 accord — known as Geneva 1 — means that Assad must step down immediately. Western powers say that it does.
Russian Foreign Minister Sergei Lavrov repeated Moscow's opposition to "outside players" meddling. But he also said Iran — Assad's main foreign backer — should have a say as world powers tried to prevent the bloodshed spilling across borders.
U.S. Secretary of State John Kerry insisted: "We see only one option, negotiating a transition government born by mutual consent. That means that Bashar Assad will not be part of that transition government.
"There is no way, no way possible, that a man who has led a brutal response to his own people can regain legitimacy to govern."
Iran was not represented. A last-minute invitation from Ban to attend was revoked on Monday after the Syrian opposition threatened to boycott the talks.
Iranian President Hasan Rouhani said that made it unlikely the conference could succeed: "Because of the lack of influential players in the meeting, I doubt about the Geneva 2 meeting's success in fighting against terrorism … and its ability to resolve the Syria crisis," Rouhani said.
"The Geneva 2 meeting has already failed without it even being started," he said IRNA news agency reported — though he added he would be pleased if it did help bring peace.
The release on the eve of the talks of thousands of photographs apparently showing prisoners tortured and killed by the government was cited by Jarba and Western ministers. The president, who succeeded his father 14 years ago, insists he can win re-election and can defeat "terrorism."
Assad has been protected by Russia, his main arms supplier, which dislikes Western attempts to overthrow incumbent leaders.
But Washington and Moscow share alarm at the spread of the violence that has already killed more than 130,000 Syrians. Having set aside their differences last year to co-sponsor the talks that are finally getting under way, Russia and the U.S. profess an urgent common goal of halting the bloodshed.
"It is hard to have expectations at the back of all this," said a source at the talks who has advised the opposition. "But Moscow and Washington are genuine on ending the conflict. They are sincere and this meeting is not for show."