UN-brokered peace talks between Yemen's internationally recognised government and the country's Shiite rebels have started in Switzerland.
The difficulty of the task was underscored by rebel fighters' failure to honour a week-long ceasefire in some parts of the country.
The ceasefire, scheduled to start at noon on Tuesday, was meant to give the warring factions a chance to find a solution to the conflict that has collapsed the Arab world's poorest country.
However, rebel shelling and ground clashes continued in the south-western Taiz province, according to security officials who remain neutral in the conflict that has splintered the country.
They said that air strikes by a Saudi-led coalition targeting the rebels have halted.
Yemen has been torn by fighting pitting the rebels, known as Houthis, and army units loyal to former president Ali Abdullah Saleh against an array of forces.
This includes the internationally recognised government - which is backed by the Saudi-led coalition and supported by the United States - as well as southern separatists, religious extremists and other militants.
UN special envoy for Yemen Ismail Cheikh Ahmed said the talks in Switzerland "should mark the end of military violence in Yemen".
He added: "The people of Yemen are daily, indeed hourly, anticipating the outcome of these discussions. This meeting is their only glimmer of hope and must not be extinguished.
"The tongues of fire, the scenes of destruction, the reverberation of bombs and the soaring prices have turned their daily lives into a series of ongoing tragedies."
UN spokesman Ahmad Fawzi said a total of 24 people were taking part in the "open-ended" talks.
According to the UN, the war in Yemen has killed at least 5,884 people since March, when the fighting escalated after the Saudi-led coalition began launching air strikes targeting the rebels.
Past efforts to end the violence have ended in failure, as the government insisted the Houthis comply with a UN resolution that requires them to return seized weapons and territory they had captured over the past year, including the capital, Sanaa.
In response, the Houthis demanded negotiations over the country's political future.
The two sides had initially agreed to halt fire at midnight on Monday but the coalition delayed the truce to midday on Tuesday, without elaborating.
Both sides of the conflict confirmed permission for "unconditional movement of supplies, personnel and teams to all parts of the country" during the ceasefire, the World Health Organisation's (WHO) mission chief for Yemen told reporters on Tuesday.
Dr Ahmed Shadoul said the WHO had 19 supply trucks ready to move in the Yemeni cities of Sanaa and Aden.
He said 150 tons of supplies located across the Red Sea in Djibouti could be delivered by next week.
It was not immediately clear if deliveries were affected because of the fighting in Taiz.
The talks are taking place at the Swiss Olympic House in the village of Macolin, a training centre for elite athletes.