A massive prisoner exchange between Yemen and Saudi Arabia began on Friday, with the first plane leaving Sanaa for Aden, according to the International Committee of the Red Cross.

ICRC media advisor Jessica Moussan told AFP that the first plane had officially left Sanaa in a 3-day process that will release roughly 900 prisoners, most of whom were fighting with the Sanaa government forces.

Yemen has been under an international war waged mainly by Saudi Arabia and the United Arab Emirates, and backed by the United States, though there have been peace talks signaling that the end of the war is on the horizon.

On Friday, more than 300 Yemeni detainees will fly between the two cities. Detainees will be released later in Marib and Mokha, as well as Riyadh and Abha in neighboring Saudi Arabia.

The exchange demonstrates a reduction in tensions following a visit from a Saudi delegation to Sanaa to meet with high-ranking officials from the Ansar Allah movement to discuss further details of the ceasefire agreement.

The war on Yemen has led to one of the world’s largest humanitarian crises and left more than 200,000 civilian casualties.

Yemen has constantly affirmed that Saudi Arabia is not a mediator in the peace proposal but a major party in the conflict. Both sides only consented to a ceasefire that was mediated by the UN last year.