Hopes were high that the talks wouldn't deteriorate into further violence as in the past, and that the prisoner exchange would be an important first step toward building confidence between highly distrustful adversaries.
The 3-year-old conflict pits the internationally recognized government, which is backed by a Saudi-led coalition, against Shiite rebels known as Houthis, who took the capital of Sanaa in 2014. The Saudis intervened the following year.
U.N. envoy Martin Griffiths said the two sides have signaled they are serious about de-escalating the fighting through calls they've made in recent weeks, and urged them to work to further reduce the violence in the Arab world's poorest nation, scene of massive civilian suffering.
"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," Griffiths said from the venue. "It will allow thousands of families to be reunited, and it is product of very effective, active work from both delegations."
The international Red Cross said it would oversee the prisoner exchange, which is expected to take weeks.
The talks in the Swedish town of Rimbo, north of Stockholm, aim to set up "a framework for negotiations" on a future peace agreement, Griffiths said, calling the coming days a milestone nonetheless and urging the parties "to work in good faith ... to deliver a message of peace."
The fighting in Yemen has generated the world's worst humanitarian crisis and claimed at least 10,000 lives, with experts estimating a much higher toll.
The Saudi-led group has conducted thousands of airstrikes, hitting schools, hospitals and wedding parties in what critics call reckless bombardment. The Houthis have, for their part, fired long-range missiles into Saudi Arabia and targeted vessels in the Red Sea. Both sides stand accused of war crimes.
U.N. officials, however, have sought to downplay expectations from the talks, saying they don't foresee rapid progress toward a political settlement but hope for at least minor steps that would help to address Yemen's worsening humanitarian crisis and prepare a framework for further negotiations.
U.N. Secretary-General Antonio Guterres welcomed the talks and urged the parties to make progress on the agenda outlined by Griffiths, U.N. spokesman Stephane Dujarric said in New York.
The U.N. chief appealed to the warring parties "to continue the de-escalation of (the key port city of) Hodeida and explore other measures to mitigate the life-threatening economic and humanitarian situation," Dujarric said.
Some Yemeni voices on both sides fired off last-minute demands, sniping commentary and finger-pointing, while combat continued on the ground in some areas.
Fighting raged in the central city of Taiz, long a contested battleground, where residents were hopeful yet highly skeptical they had much to look forward to amid the poverty.
"We here in Taiz have been three years without salaries, and still we are here in the street, looking for an income," said local Faisal al-Asali from a street cafe.
Griffiths said the talks would address several main points mentioned by both sides: broader prisoner exchanges, the release of funds to the central bank to pay civil servants in rebel-controlled territory, a possible handover of the port at Hodeida to the U.N., and rebel calls to lift the coalition's blockade of Sanaa airport to commercial traffic.
"I believe that we can also here in the coming days find solutions on specific issues that will improve cooperation and reduce suffering," he said.
Both the internationally recognized government, which is backed by the U.S.-sponsored Saudi-led coalition, and the Iran-aligned Houthi rebels say they are striving for peace.
The Houthi delegation arrived in Stockholm late Tuesday, accompanied by Griffiths. The government delegation and the head of the rebel delegation travelled to Sweden on Wednesday.
Meanwhile, the U.N. food agency said Thursday it is planning to rapidly scale up food distribution to help another 4 million people in Yemen over the next two months, more than a 50-percent increase in the number reached now - if access can be maintained in the war-stricken country.
World Food Program spokesman Herve Verhoosel said the "ambitious undertaking" finalizes plans in the works in recent months to reach 12 million people with food and nutritional supplements through January, up from between 7-8 million now.
The target population includes some 3 million women and children who need special support to prevent malnutrition. Verhoosel said the rollout will require "safe, immediate and unimpeded access for food and other vital supplies."
Twenty million people, or 70 percent, of Yemenis are "food insecure," U.N Humanitarian Coordinator Lisa Grande said, meaning they do not have reliable access to sufficient amounts of nutritious food.
Sweden's foreign minister who opened the talks, Margot Wallstrom, wished the Yemen adversaries strength to find "compromise and courage" as they embark on the difficult task ahead.
"Now it is up to you, the Yemini parties," she said. "You have the command of your future."
Rohan reported from Cairo. Associated Press writers Jamey Keaten in Geneva and Edith M. Lederer at the United Nations contributed to this report.
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