Warring factions in Yemen will relaunch peace talks on December 15, the UN envoy to the embattled country said Monday, voicing confidence that a temporary ceasefire will be in place before negotiations begin.

Talks to ease the violence in Yemen have been stalled for months, with the conflict escalating since March when a pro-government coalition led by Saudi Arabia began bombarding Iran-backed Huthi rebels.

With the humanitarian crisis in the impoverished country deteriorating, UN envoy Ismail Ould Cheikh Ahmed said a swift halt to the fighting was imperative for those caught up in what has increasingly become a regional conflict.

Ahmed told reporters that three delegations would take part in talks likely to be held outside Geneva which have no definitive timeline and will last "as long as it takes."

The delegations include representatives of President Abedrabbo Mansour Hadi's government, the Huthi rebels, and officials from the General People's Congress (GPC), who are loyalists of former president Ali Abdullah Saleh.

Though not formally aligned, some GPC members have expressed support for the Huthis.

The UN envoy further said he was "almost certain" a temporary ceasefire would be in force by December 15 "in order to create an environment conducive to peace talks."

"Everyone seems to be welcoming this idea that we will have a ceasefire," Ahmed said, noting that a permanent ceasefire remained a more distant prospect and would depend on the outcome of negotiations.

According to the UN envoy, Riyadh said it would observe a ceasefire and pause its aerial assault so long as Hadi was on board with the plan.

- Key governor killed -

Each delegation will be made up of 12 members, including eight official negotiators and four advisors.

The delegations have not yet been finalised, in part because the UN has insisted that more women be included, according to Ahmed.

Asked about reports that Huthi rebel leaders had been dragging their feet and refusing to name their delegates in an apparent bid to further stall dialogue, the UN envoy said he was certain that the Iran-backed faction would show up.

Talks will focus on four main areas, including the terms for a permanent ceasefire and the withdrawal of armed groups from the areas under their control.

Another area of dialogue was described as "confidence-building measures" which includes broadening humanitarian access in the country where aid workers have been killed and kidnapped.

Finally, delegates will try to hammer out a political future for Yemen, a country plunged into worsening chaos since the insurgents overran the capital Sanaa, forcing the government to flee to Saudi Arabia.

Jihadist groups have exploited the conflict by making sweeping gains.

The announcement on the restart of talks came after the killing of the governor of Yemen's second city Aden, Jaafar Saad, in an attack claimed by the Islamic State jihadist group, which has threatened further violence.

The assassination happened a day after the UN envoy visited Aden.

Ahmed said he was "extremely concerned by the ever-growing suffering of the Yemeni people" and called on the rival camps to show "courage, personal sacrifice and tenacity" in the bid for peace.

The United Nations says more than 5,700 people have been killed in Yemen, almost half of them civilians, since the Saudi-led air campaign began.