Yemen's warring factions confirmed their agreement on Thursday to a temporary humanitarian ceasefire set to begin on Friday (July 10) night, United Nations envoy Ismail Ould Cheikh Ahmed said.

The pause in the fighting will last about a week until the end of the Muslim holy month of Ramadan and aims to allow the delivery of assistance to some of the 21 million Yemenis in need.

The UN has worked intensively to broker a ceasefire to halt more than three months of many-sided fighting inside the country and Saudi-led air strikes against the Houthis and their army allies that have killed more than 3,000 people.

"For the humanitarian pause, we are going to start tomorrow evening and we have assurances from all the parties, and we are quite optimistic it will be respected," Ould Cheikh Ahmed told Reuters by phone from Ethiopia, after finishing discussions in the Houthi-held Yemeni capital Sanaa.

"We have agreed to go ahead, based on two major points. The first is the commitment of all parties not to violate this ceasefire, this humanitarian pause. The second is that humanitarian assistance can reach all parts of Yemen," he added.

Relief agencies say the fighting and a near-blockade imposed by an alliance of Arab states, aimed at stopping weapons deliveries to the Houthis, have caused a humanitarian disaster in Yemen, with over 80 percent of its 25 million people now needing some form of emergency aid.

Rights groups have also condemned local blockades by armed groups on supplies headed for war-torn civilian areas.

CHALLENGE

Yemen's president Abd-Rabbu Mansour Hadi, in exile in Saudi Arabia, has asked the U.N. for "guarantees" to help the truce succeed, which include prisoner releases by the Houthis and withdrawals from vast areas where it is battling local fighters.

Implementing more thorny political points, the envoy said, would not happen immediately and required more discussion, but the Houthis have released a top pro-Hadi politician in Sanaa and allowed the shipment of 50 aid trucks to the embattled southern city of Aden to buttress the truce.

A senior Western diplomat said the intensity of battles raging nationwide would render a swift calm difficult.

"It is still going to be a challenge to have this call heeded within the next 24 hours because of the entrenched fighting on the ground," the diplomat told Reuters.

News of the expected truce helped lift the Saudi stock market. The index closed 2.5 per cent higher.

Saudi Arabia and an Arab coalition have been bombing the Houthis and their allies in Yemen's army in an effort to restore Hadi and bolster armed opponents of the Iran-allied Houthis.

The Houthis, who took over the capital Sanaa last September, deny Saudi accusations that they are an Iranian proxy and describe their armed advance throughout Yemen as a revolution against a corrupt government backed by the West.

The group has previously said it welcomed any ceasefire but has yet to accept a UN Security Council Resolution passed in April which recognises Hadi as the legitimate president and calls on them to quit seized land.

The United States fears the turmoil will strengthen al Qaeda in the Arabian Peninsula, the deadliest branch of the global militant group.

AQAP's new leader Qassim al-Raymi, appointed after his predecessor was killed in U.S. drone strike last month, called for attacks on the United States in a taped speech released on Thursday. - Reuters