Yemen's Houthi rebels have unilaterally released 290 detainees as part of a UN peace initiative, the International Committee of the Red Cross says, BBC reports.
Those freed include 42 survivors of an air strike on a prison this month that killed more than 100 people.
The attack was carried out by a Saudi-led coalition backing the Yemeni government in the country's civil war.
The UN special envoy for Yemen said he hoped the Houthis' step would lead to further releases by both sides.
A prisoner swap was one of three elements of an agreement between the warring parties that was brokered by the UN in Sweden's capital, Stockholm, in December.
The head of the Houthi committee for prisoner-of-war affairs, Abdul Qader al-Murtada, said on Monday the rebels would free 350 detainees, including three unidentified Saudi nationals.
"Our initiative proves our credibility in implementing the Sweden agreement and we call on the other party to take a comparable step," he added.