The UN envoy to Syria called on Wednesday for "free and fair" elections after the ouster of president Bashar al-Assad, voicing hope for a political solution for Kurdish-held areas.

Assad fled Syria following a lightning offensive spearheaded by the Islamist Hayat Tahrir al-Sham (HTS), more than 13 years after his crackdown on democracy protests precipitated one of the deadliest wars of the century.

He left behind a country scarred by decades of torture, disappearances and summary executions, and the collapse of his rule on December 8 stunned the world and sparked celebrations around Syria and beyond.

Years of civil war have also left the country heavily dependent on aid, deeply fragmented and desperate for justice and peace.

Addressing reporters in Damascus, UN special envoy Geir Pedersen said "there is a lot of hope that we can now see the beginning of a new Syria".

"A new Syria that... will adopt a new constitution... and that we will have free and fair elections when that time comes, after a transitional period," he said.

Calling for immediate humanitarian assistance, he also said he hoped to see an end to international sanctions levied against Syria over Assad's abuses. (AFP)