At the end of the meeting, the 17-nation International Syria Support Group (ISSG) -- co-chaired by the US and Russia -- vowed to bolster the ravaged nation's shaky ceasefire and send humanitarian relief.
However, the group also admitted it had been unable to set a fresh date for negotiations between the regime of President Bashar al-Assad and the Syrian opposition.
But de Mistura insisted: "There is hope" despite the slow progress.
"I can feel sufficient comfort to explain to the Syrian people and to the international community that we can re-launch the talks... because it is clear there is no military solution," he told reporters in the Austrian capital.
"But we need to do it soon, not late, otherwise we lose the momentum," the UN envoy said.
He said negotiators had to "bear in mind" that the month-long Muslim fasting month of Ramadan would start around June 6 "in that part of the world".
After Tuesday's talks, de Mistura had warned the UN-mediated talks in Geneva would have little purpose if the killing continued.
The Syrian conflict erupted in early 2011 when Assad's forces staged a brutal crackdown on anti-government protests, sparking violence that has since claimed more than 270,000 lives.
Millions have been driven from their homes and hundreds of thousands of refugees have flooded into Europe, sparking a humanitarian and political crisis.
- Consequences for violations -
On the ground, US allies like Saudi Arabia and Turkey back some of the rebel factions, while Russia has dispatched war planes and advisors to back Assad, who is also supported by troops from Iran.
In late February, Washington and Moscow chivvied regime and rebel forces into agreeing a shaky ceasefire, but pockets of violence remain.
On Tuesday, the ISSG said there would be consequences for parties breaching the truce and pledged to maintain pressure on Assad.
Washington regularly accuses the Syrian strongman of violating the truce and of bombing civilians, whereas Russia blames rebel factions for carrying out massacres.
Divisions between the two world powers have hampered efforts to agree a framework, under which Syria would "transition" away from Assad's rule.
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However, the group also admitted it had been unable to set a fresh date for negotiations between the regime of President Bashar al-Assad and the Syrian opposition.
But de Mistura insisted: "There is hope" despite the slow progress.
"I can feel sufficient comfort to explain to the Syrian people and to the international community that we can re-launch the talks... because it is clear there is no military solution," he told reporters in the Austrian capital.
"But we need to do it soon, not late, otherwise we lose the momentum," the UN envoy said.
He said negotiators had to "bear in mind" that the month-long Muslim fasting month of Ramadan would start around June 6 "in that part of the world".
After Tuesday's talks, de Mistura had warned the UN-mediated talks in Geneva would have little purpose if the killing continued.
The Syrian conflict erupted in early 2011 when Assad's forces staged a brutal crackdown on anti-government protests, sparking violence that has since claimed more than 270,000 lives.
Millions have been driven from their homes and hundreds of thousands of refugees have flooded into Europe, sparking a humanitarian and political crisis.
- Consequences for violations -
On the ground, US allies like Saudi Arabia and Turkey back some of the rebel factions, while Russia has dispatched war planes and advisors to back Assad, who is also supported by troops from Iran.
In late February, Washington and Moscow chivvied regime and rebel forces into agreeing a shaky ceasefire, but pockets of violence remain.
On Tuesday, the ISSG said there would be consequences for parties breaching the truce and pledged to maintain pressure on Assad.
Washington regularly accuses the Syrian strongman of violating the truce and of bombing civilians, whereas Russia blames rebel factions for carrying out massacres.
Divisions between the two world powers have hampered efforts to agree a framework, under which Syria would "transition" away from Assad's rule.
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