A damaged house in Sanna,Yemen (Picture: PA).
Peace talks aimed at ending nearly four years of civil war in Yemen are continuing in Sweden.
The UN envoy for Yemen, Martin Griffiths, says it is a critical opportunity to give momentum to the peace process.
His team is working alongside delegations from the Yemeni government and the Houthi rebels to enable the informal talks which are due to last a week.
Martin Griffiths said the coming days were a milestone and urged the parties not to "waver... let us work in good faith ... to deliver a message of peace".
He told delegations from the government and the Houthi rebels that they held the future of their country in their hands.
The government is backed by a Saudi-led coalition and the Houthi rebels are aligned with Iran.
Mr Griffiths said both sides have signalled they were serious about de-escalating the fighting through calls they have made in recent weeks, and urged them to work to further reduce the violence.
He gave details of a prisoner exchange as a first step toward building confidence.
"I'm also pleased to announce the signing of an agreement on the exchange of prisoners, detainees, the missing, the forcibly detained and individuals placed under house arrest."
"It will allow thousands of families to be reunited, and it is the product of very effective, active work from both delegations."
UN officials say they do not expect rapid progress toward a political settlement but hope for at least minor steps that would help to address the worsening humanitarian crisis.
The main aim is to prevent the Yemeni Government launching an all-out attack on the key port city of Hudaydah, which is controlled by the rebels.
The war has caused the world's worst humanitarian crisis in recent times.
Thousands of people have died in fighting and millions have been pushed to the brink of starvation.
According to the UN at least 6,660 civilians have been killed and 10,560 injured in the war. It also says half the population, 14 million people, are facing pre-famine conditions.
These are the first peace talks since 2016. The last attempt at a negotiated peace collapsed in September when the Houthis failed to show up for talks in Geneva.