Yemeni journalists hold placards to support their colleagues jailed in Shiite Houthi rebels prisons in Yemen during a press conference of the United Nations Special Envoy to Yemen on May 5, 2016 at the information ministry in Kuwait City. The head of the Yemeni government delegation at troubled peace talks in Kuwait demanded action from UN mediators over rebel shelling of besieged third city Taez. / AFP PHOTO / YASSER AL-ZAYYAT

Warring parties in Yemen reached a preliminary agreement on Tuesday to release all prisoners beginning within 20 days, sources at U.N.-backed peace talks in Kuwait said.

The agreement is one of the most important milestones yet in nearly three weeks of negotiations that have in recent days struggled to maintain a ceasefire on the ground and appeared headed for collapse.

A Saudi-led coalition intervened in Yemen’s conflict a year ago, mainly with air strikes in support of the country’s internationally-recognised government.

A tentative U.N-backed ceasefire has been in place since last month to give the peace talks in Kuwait a chance, but both sides have regularly accused each other of violations.