A “sound plan” for a nationwide ceasefire in Yemen has been before Houthi leadership for “a number of days,” but it appears the group is prioritizing a military offensive to take Marib, the US special envoy on Yemen, Tim Lenderking, said on Friday. “I will return immediately when the Houthis are prepared to talk,” Lenderking told the Atlantic Council think tank after a 17-day visit to the region to revive efforts to end the six-year conflict that is widely seen as a proxy war between Saudi Arabia and Iran. “The US and U.N. – we urge the Houthis to respond,” he said. “If we cannot make progress now, the country will spiral into greater conflict and instability.” A Saudi Arabia-led military coalition intervened in Yemen in 2015 after the Iran-allied Houthi group ousted the country’s government from the capital Sanaa. The Houthis say they are fighting a corrupt system. “We now have a sound plan for a nationwide ceasefire with elements that would immediately address Yemen’s dire humanitarian situation directly,” Lenderking said. “That plan has been before the Houthi leadership for a number of days.”