RIMBO, Sweden (AP) — Representatives from Yemen's warring sides sat in the same room for the first time in years on Thursday in Sweden as U.N.-sponsored peace talks aimed at halting a catastrophic three-year war opened to great hopes but also high skepticism.

In a positive sign, the U.N. envoy said the sides had agreed on a prisoner exchange as a first step toward building confidence.

Martin Griffiths also said the two sides have signaled they were 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 civilians suffering.

The talks in the Swedish town of Rimbo, north of Stockholm, aim to setup "a framework for negotiations" on a future peace agreement, Griffiths said, calling the coming days were a milestone nonetheless and urging the parties "to work in good faith ... to deliver a message of peace."

"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 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 conflict pits the internationally recognized government, which is backed by a Saudi-led coalition, against Shiite rebels, known as Houthis.

During the three-year war, Saudi-led airstrikes have hit schools, hospitals and wedding parties, and the Houthis have fired long-range missiles into Saudi Arabia and targeted vessels in the Red Sea.

U.N. officials, however, have sought to downplay expectations from the talks, saying they don't expect rapid progress toward a political settlement but hope for at least minor steps that would help to address Yemen's worsening humanitarian crisis.

Yemeni voices from both sides continued to make some last-minute demands and accusatory finger-pointing, while minor fighting continued to some extent on the ground.

Griffiths said the talks would address several main points mentioned by both sides: prisoner exchange, the release of funds to the central bank to pay civil servants in rebel-controlled territory, a possible handover of the port city of Hodeida to the U.N., and the reopening of the blockaded airport in the capital, Sanaa, to aid deliveries.

"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 a U.S.-sponsored and 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 poor, war-stricken country.

World Food Program's 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, 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."

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."

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Rohan reported from Cairo. Associated Press writer Jamey Keaten in Geneva contributed to this report.