The Syrian Foreign Minister and the UN Secretary-General have clashed at the start of crucial peace talks aimed at ending the country's bloody civil war.

Walid al Muallem ignored Ban Ki-moon's appeal for him to end an opening speech that lasted more than 30 minutes, saying "You live in New York. I live in Syria. I have the right to give the Syrian version here in this forum".

He also launched a blistering attack on the Syrian opposition, asking them "Where is your vision for this great country? Where are your ideas? Where is your political programme? What are the tools on the ground? I am quite sure you have nothing".

Mr. Ban said the "constructive mood" with which the talks began had been shattered and warned: "I hope this will not be repeated".

The diplomatic battle to end Syria's bloody civil war is underway in Switzerland, as opposition delegates sit down with government representatives for the first time in three years.

International delegates have gathered in the city of Montreux, on the banks of Lake Geneva, for talks aimed at ending a conflict which has killed more than 100,000 people.

The peace talks are going ahead despite a last-minute dispute over the United Nations' decision to withdraw an invitation to Iran.

The exclusion of the Islamic Republic from the conference has highlighted tensions between the West and Russia over how to broker an agreement to end the violence.

Iran is the main ally of Syrian President Bashar al-Assad. The country's exclusion came after Tehran refused to endorse a UN-backed plan for a transitional governing body in Syria.

The issue of transition of power is expected to be central to the success of the talks, which have been dubbed "Geneva 2". The Western-backed opposition has demanded that Mr. Assad must quit and face a war crimes trial.

But the Syrian Foreign Minister, Walid al Moualem, has rejected any discussion of Mr. Assad being forced to step down.

"The subject of the president and the regime is a red line for us and the Syrian people and will not be touched," he said on the eve of the talks, according to the SANA news agency.

Opening the summit UN Secretary-General Ban Ki-Moon told delegates they have an enormous opportunity and responsibility to render a service to the people of Syria.

The conference also begins in the shadow of allegations of large-scale torture and execution of prisoners by government forces.

The day before the talks, a group of international lawyers published allegations of the "systematic torture and killing" of up to 11,000 people by the Syrian regime.

Fatima Khan, the mother of British doctor Abbas Khan, who died in a Syrian prison last month, said the reports of torture and execution were no surprise.

"I'm not surprised with the report. I knew...all this" she said.

"I heard my son was living with 9,000 other prisoners and my son told me that every day they used to take two or three (and) torture them. Either one comes back or two comes back, or none of the three comes back. I knew this. My son was only a humanitarian aid worker. Why was he tortured?"

"If that regime is so cruel (that) they have no brains and no heart to understand (the difference between) a humanitarian aid worker and a terrorist, then they should not stay in power" she added.

At the summit US Secretary of State John Kerry said the only option is a transitional government without the country's current leader.

The British Foreign Secretary William Hague urged both sides in Syria to "seize the chance" to end the civil war as he arrived in Switzerland.

"Opposition has been tested and has come. Now regime must be tested on willingness to seek a political solution" Mr. Hague wrote on Twitter.

Mr. Hague added that it was a "great shame" that Iran - which has enjoyed a thawing of relations with the West in recent months - had failed to endorse the principles of the talks.

US President Barack Obama and Russia's Vladimir Putin had a "business-like" conversation about the Syrian conflict by phone on Tuesday.

Russian Foreign Minister Sergei Lavrov also met the US Secretary of Statein Montreux ahead of today's opening of negotiations.

CEO of Concern, Dominic McSorley, has told the Pat Kenny Show here on Newstalk that they need to reach an agreement on a sustained end to violence.