An exchange of more than 800 prisoners linked to Yemen’s long-running war began on Friday, the International Committee of the Red Cross said.

The UN-brokered deal, in the works for months, comes amid concerted diplomatic efforts to negotiate an end to the conflict.

It is most significant prisoner exchange in Yemen since both sides freed more than 1,000 detainees in October 2020.

Thousands of people are believed to be held as prisoners of war by all sides since the war erupted.

In the three-day exchange, flights will transport prisoners between Saudi Arabia and Yemen’s capital, Sanaa, long held by the Iranian-backed Houthi rebels, said Majed Fadail, a deputy minister for human rights for Yemen’s internationally recognised government.

Other flights will take prisoners between Sanaa and other Yemeni cities controlled by the government, he said.

The Red Cross said that on Friday there would be two rounds of simultaneous flights between Aden and Sanaa to transfer prisoners.

Yemen’s conflict began in 2014 when the Houthis seized Sanaa and much of the country’s north. Yemen’s internationally recognised government fled to the south and then into exile in Saudi Arabia.

The Houthi takeover prompted a Saudi-led coalition to intervene months later.

The conflict has in recent years turned into a regional proxy war between Saudi Arabia and Iran, with the United States long involved on the periphery, providing intelligence assistance to the kingdom.

However, international criticism over Saudi airstrikes killing civilians saw the US pull back its support.

The war has killed more than 150,000 people, including fighters and civilians, and created one of the world’s worst humanitarian disasters.

The prisoner exchange had been scheduled to start earlier in the week but was delayed because of apparent logistical reasons.

“With this act of goodwill, hundreds of families torn apart by conflict are being reunited during the holy month of Ramadan, a glimmer of hope amidst great suffering,” Fabrizio Carboni, the Red Cross’ regional director for the Near and Middle East, said in a statement.

“Our deep desire is that these releases provide momentum for a broader political solution, leading to even more detainees returning to their loved ones.”

The deal tentatively calls for the Houthis to release more than 180 prisoners, including Saudi and Sudanese troops fighting with the Saudi-led coalition, and four Yemeni journalists.

The journalists were detained in recent years and sentenced to death by a Houthi-controlled court in a trial described by Amnesty International as “grossly unfair”,

The deal also will see the release of top military officials held by the Houthis since the start of the war.

In return, the Saudi-led coalition and Yemeni government are scheduled to release more than 700 Houthi prisoners, the rebels said.

Saudi Arabia has already freed 13 Houthi detainees who returned to Sanaa on April 9 ahead of a trip by Saudi ambassador to Yemen, Mohammed bin Saeed al-Jaber, to the Yemeni capital.

Including those detainees, the deal will see a total of 869 prisoners released, the Red Cross says.