The UN’s Syria envoy Staffan de Mistura expressed optimism on Wednesday that the stalled peace talks could resume, but stressed it had to happen in "soon" to avoid losing momentum.

The UN's Syria envoy Staffan de Mistura expressed optimism on Wednesday that the stalled peace talks could resume, but stressed it had to happen in "soon" to avoid losing momentum.

His comments came a day after talks between world powers on ending the five-year conflict failed to make a clear breakthrough in Vienna.

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 Syrian government and the foreign-backed 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.

On Tuesday, the ISSG said there would be consequences for parties breaching the truce and pledged to maintain pressure on Assad.