The UN envoy to Yemen, Martin Griffiths, on Thursday hailed efforts by the country’s warring parties to implement one of the biggest prisoner exchanges of its kind in the world. Yemen’s internationally recognised government and Houthi rebels agreed last month to exchange 1,061 detainees as part of UN-led efforts to end the five-year conflict. “This is an extraordinary number to be released during conduct of hostilities. Indeed, some say, it may well be the largest such operation of this kind in the history of prisoner release,” Mr Griffiths told the UN Security Council. “Since this morning, the skies of Yemen have seen an airlift of hope,” he said shortly after the operation commenced. The UN envoy, who brokered peace talks in Sweden two years ago, said thousands of other men were still detained and an agreement must be made to release them. “We will soon convene the parties to discuss more releases, in line with the commitment they made in Stockholm in December 2018 to release all conflict-related prisoners and detainees,” he said. Mr Griffiths also called on the warring sides to "unconditionally and immediately release all arbitrarily detained civilians, including journalists and political prisoners". Planes carrying prisoners left Sanaa, the Houthi-held capital, and Sayoun Airport in government-held Hadramawt province on Thursday morning. The International Committee for the Red Cross, which is overseeing the swap, said its teams were present as the operation began. "We saw the joy and happiness of fathers, husbands and brothers returning home. Each individual family reunification is a positive step; taken as a whole, we hope this operation allows the sides to come one step closer to a resolution that could end the suffering endured by so many in this conflict," Fabrizio Carboni, the ICRC regional director for Near and Middle East, told <em>The National</em>. Mr Carboni said the ICRC was hopeful that more detainee releases may take place. "This positive and hopeful operation today builds confidence, which may very well lead to more such releases in the future, and perhaps even lead to renewed peace talks," he said. In total two planes left Abha in Saudi Arabia for Sanaa. In Yemen, three flights left Sanaa, two internal fights to Seyoun and one to Riyadh, and two flights carried detainees from Seyoun to Sanaa, said Ruth Hetherington, an ICRC spokesperson. "In total, seven flights took place on five planes, and more than 700 detainees were released during the first day's more than 12-hour long operation," Ms Hetherington told <em>The National</em>. The exchange is expected to continue on Friday with the release of hundreds of other prisoners. Mr Griffiths said early Thursday that the prisoner swap was "another sign that peaceful dialogue can deliver". "I hope the parties will soon reconvene under UN auspices to discuss the release of all conflict-related prisoners and detainees." Yemen’s warring parties agreed to a prisoner swap during 2018 peace talks in Sweden that would allow for the eventual exchange of 15,000 people. It was hailed as a breakthrough in a conflict that has caused the world's worst humanitarian crisis. Sporadic prisoner swaps have taken place since then. The prisoner swap was part of several confidence-building measures to pave the way for talks to end the civil war. A government official told <em>The National</em> that technical difficulties occurred before Thursday's exchange began, raising concerns that it might not proceed. “We had fears that the operation will not go through and we were not fully assured until everything was complete because the Houthis have no guarantor and take no responsibility or liability for their actions,” Majed Fadhil, Yemen’s deputy human rights minister and member of the government’s prisoner swap committee, said. The committee convened in Geneva in September and reached a deal to swap 1,081 detainees. The rebels released 400 government prisoners on Thursday, including 15 Saudi and four Sudanese citizens. The Saudi-backed government freed 681 Houthi fighters, a member of the government delegation said. The prisoner swap came a day after two Americans and the remains of a third who died while being held captive by the rebels were released in exchange for the return of about 250 Houthi men from Oman. For months Mr Griffiths has been pushing all sides to agree to a ceasefire deal that would pave the way for broader talks to end the war. The conflict erupted in late 2014 when the Houthis seized Sanaa and much of the country’s north. A Saudi-led Arab Coalition intervened the following year in an effort to restore the government of President Abdrabu Mansur Hadi to power.