The UN special envoy for Syria faced an uphill task in Geneva on Monday to get talks to end the brutal civil war off the ground, as the opposition hesitated to join negotiations with the regime.
The urgency to find a solution to the four-year war was brought home Sunday when multiple explosions killed 71 people near a revered Shiite shrine outside the capital Damascus, according to a Britain-based monitor.
The blasts were claimed by Islamic State (ISIS), the extremist group that is running swathes of Syria and Iraq which has launched attacks worldwide, including in Paris in November when 130 people were murdered.
EU foreign policy chief Federica Mogherini said the new atrocity in Syria was "clearly aimed to disrupt the attempts to start a political process".
The deaths added to the more than 260,000 people to have perished since 2011 in a highly complex conflict sucking in a host of outside powers -- and on different sides.
Half the population has been displaced, seeking refuge in neighbouring countries or risking their lives to make it to Europe, creating a major political headache there.
Present in Geneva are the main opposition umbrella group the High Negotiation Committee (HNC) and representatives of President Bashar al-Assad.
Under an ambitious roadmap agreed in November in Vienna by all the outside powers embroiled in the war, the "proximity talks" -- so not face-to-face -- are due to last six months.
The plan envisions elections within 18 months, but the key question of the future of Assad -- backed by Iran and Russia -- was left until later to resolve.
But the Saudi-backed HNC is refusing to play ball unless Assad's regime first allows humanitarian access to besieged towns, stops bombarding civilians and releases prisoners.
A Western diplomat said that on Sunday UN envoy Staffan de Mistura made proposals to a mistrustful HNC in talks in a Geneva hotel, but that they were still hesitating.
"We only came to Geneva after written commitments on the fact that there would be serious progress on the humanitarian issues," HNC spokeswoman Basma Kodmani told reporters on Sunday.
"We are here for political negotiations but we cannot start those until we have those gestures," she said.
But Damascus's chief negotiator Bashar al-Jaafari -- who met de Mistura on Friday -- on Sunday called the opposition "not serious".
"We do not know who is the other side. They don't even have a final list," the tall and stern Syrian ambassador to the UN told a packed news conference.
US Secretary of State John Kerry urged on Sunday both sides "to make the most of this moment" in an online statement broadcast from Washington.
Kerry urged the opposition to drop their preconditions, but also had hard words for their foes, accusing Assad's forces of deliberately starving besieged towns.
He described the talks in Geneva as being at a "pivotal phase" and said the HNC represented an "inclusive opposition."
Another thorny issue is which rebel groups will be involved in the talks, although all sides agree on the exclusion of IS and Al-Nusra Front, Al-Qaeda's Syrian branch.
The powerful Army of Islam rebel group is part of HNC's delegation to Geneva, and the HNC's chief negotiator and Army of Islam member Mohammed Alloush was expected in Geneva on Monday.
The choice of Alloush has been controversial, with Syria's ally Moscow saying it considers Army of Islam as "terrorists" and other opposition groups insisting it was unacceptable for the delegation to be led by a member of an armed group.
But Alloush dismissed the criticism on Sunday. "Bashar al-Assad is the one who is the terrorist," he told AFP.
In addition, and in a potentially hopeful sign, Western diplomats said Sunday that Riad Hijab, the head of the HNC and a former Syrian prime minister, was also expected in Geneva on Monday.