MONTREUX, Switzerland: 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 US 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 UN 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.

The conference, which Ban hopes will be followed by further talks in Geneva, has raised no great expectations, particularly among Islamist rebels on Syria's frontlines who have branded Western-backed opposition leaders as traitors for even agreeing to be in the same room as Assad's delegates.

Underlining the seemingly intractable positions, Syrian Foreign Minister Walid al-Moualem said on Tuesday that Assad's position was non-negotiable.

“The subject of the president andthe regime is a red line for us and the Syrian people and will not be touched,” he was quoted as saying in Syrian media.

Iran sceptical

Lavrov, co-sponsor of the conference with Kerry, repeated Moscow's opposition to “outside players” meddling in Syria's affairs but he also said Iran — Assad's main foreign backer — should have a say.

Kerry, in his brief speech to the floor, said negotiations would be “tough and complicated” but insisted there was “no way” Assad could stay on with a transitional government.

“One man can no longer hold an entire nation or region hostage,” Kerry said, while also adding there would be no room in government for “terrorists” among the rebel forces.

Assad backer Iran was not present. A last-minute invitation from Ban to attend was revoked on Monday after the Syrian opposition threatened to boycott the talks, since Iran shares Assad's view that he should not lose power.

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 2meeting'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 was quoted as saying by IRNA news agency — though he added he would be pleased if it did help bring peace.

Clashes

As speeches began in Montreux, the war went on in Syria. The Syrian Observatory for Human Rights monitoring group reported clashes and air strikes around the country.

Around Damascus, government artillery hit villages and rebels clashes with the army in the neighbourhood of Jobar on the northeast fringe of the capital, it said.

Activists also reported clashes and in the central city of Hama, the southern province of Deraa — where the revolt began — and the northern city of Aleppo.

French Foreign Minister Laurent Fabius said on arrival: “The real conference begins in two days. If it fails it will be a real crisis.”

Suhair Attassi, a member of the opposition National Coalition, said in Montreux that Moualem's refusal to accept Assad should go meant it would be up to his Russian ally to press him to accept the international demand for a transition.

“Now there is the responsibility on Russia to put pressure on Assad,” he said. “The transition for us is the essential point. We aren't here just to talk humanitarian aid. We need a democratic transition.”

The release on the eve of the talks of thousands of photographs apparently showing prisoners tortured and killed by the government reinforced opposition demands that Assad must quit and face a war crimes trial.

The president, who succeeded his father 14 years ago, insists he can win re-election and wants to talk about fighting “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.