°®Âþµº

A new round of Syria peace talks began in Geneva on Monday, but prospects of success remain uncertain amid fundamental disputes over the both fate of Bashar al-Assad and the form of political transition the country will take when war ends.

The talks opened a day before the fifth anniversary of the outbreak of the conflict international powers are seeking to end.

It was this occasion that senior United Nations humanitarian officials used to during an appeal to both parties to end fighting and find compromise.

"We use our collective voice to call on all parties, local and international, for this anniversary to be the last one and for the political talks to bring real peace and an end to the suffering in Syria," 11 senior officials from New York, Geneva, Rome and Amman said in a joint .

As the delegations arrived in Switzerland over the weekend, Damascus warned that any discussion about removing Assad would be a "red line".

Top Western diplomats immediately condemned the comment from Syrian Foreign Minister Walid Muallem as divisive and provocative.

The Syrian opposition's delegation is preparing to submit its vision for political transition in Syria after the war, delegation chief Asad al-Zoabi told °®Âþµº.

This will be submitted on Tuesday in a meeting scheduled with the UN envoy.

What is the real issue? The mother of all issues (is) political transition. - Staffan de Mistura, UN Syria envoy

The opposition's proposal will be based on the Geneva Communique and Resolution 2254, and will demand Assad and his "clique" step down at the start of the transition, Zoabi said.

By contrast, he said, the Syrian regime's proposal for transition - submitted on Monday - focused on a war against "terrorism", and suggested forming a new government which would only include opposition figures not involved in the fight against the regime. This government would also serve under Assad, something which all members of the mainstream opposition squarely rejects.

A new constitution would be drafted before being put to a referendum, but there is no reference to presidential elections in the government's proposal, Zoabi added.

Wrangling over delegations

A lot has changed since the last round of indirect talks collapsed in February, particularly for many of Syria's war-ravaged people who have previously been deprived of regular access to life-saving aid.

A temporary ceasefire introduced on 27 February has largely held, despite accusations of violations from both sides. It has allowed aid to reach some 150,000 people living under siege, the vast majority in opposition areas.

The current ceasefire, the most significant since the conflict began, has sparked cautious encouragement.

The truce - the most significant since the conflict began - has sparked cautious encouragement.

But experts warn that negotiations will still struggle to achieve a durable peace on the fractured battlefields where multiple groups are competing for dominance.

Representatives from Syrian Kurdish groups, which have played a key role in combatting jihadi fighters, have been excluded from the talks despite a push from Russia.

Russian Foreign Minister Sergei Lavrov reaffirmed Moscow's position on Monday, saying that "the whole spectrum of Syrian political forces" should have a voice in Geneva.

"Otherwise this cannot claim to be a representative forum," he was quoted as saying by the RIA Novosti state news agency.

A second round of roughly two weeks of talks would start after a brief recess, followed by third round, at which point de Mistura said he hoped there would be a "clear roadmap" for a permanent deal.

No 'plan B'

The UN envoy acknowledged the huge divisions between the opposing sides, with Assad's fate and the prospect of holding elections standing out a key hurdles.

But, he stressed, walking away from dialogue was not an option.

"As far as I know, the only plan B available is the return to war, and to an even worse war than we had so far," he said.

Analysts have said the talks are largely a forum for international powers involved in the conflict, and that the strategic interests of the US and regime ally Russia will be crucial to determining the shape of a possible deal.

De Mistura told reporters that if progress appears impossible, he will turn to the "real peacemakers", referring to Washington, Moscow and the UN Security Council.

"We will bring the issues back to those who have influence," if negotiations go nowhere, he said.

The leverage of major powers over Syria's warring parties has its limits. Half of Syria's territory is controlled by jihadi groups from the Islamic State group or al-Qaeda affiliate al-Nusra Front, neither of which are included in the ceasefire.

Russia has continued to focus its airstrikes on territories controlled by these extremist groups since the truce came into effect last month, but Syrian activists said that many have hit non-extremist rebel groups and towns.

Agencies contributed to this story.