Gulf envoys told UN chief Ban Ki-moon on Monday that there would be no immediate ceasefire in Yemen unless Huthi rebels withdraw from seized territory.Saudi Ambassador Abdallah al-Mouallimi said "certain conditions" must be met for the Saudi-led air campaign to be suspended and that these were spelled out in the recently-adopted Security Council resolution."We all want to see an early end to the military hostilities, but there are conditions conducive to having an early end to the hostilities," told Mouallimi, following a meeting with Ban.The resolution adopted last week demands that the Shiite Huthis pull back from territory seized, including the capital Sanaa, end their violent campaign and return to peace talks.With the air strikes claiming more civilian lives, Ban has called for an "immediate ceasefire" in Yemen, saying the country was "in flames" and that it was time for a "passage to real peace."Following the resignation of Moroccan diplomat Jamal Benomar as Yemen peace envoy, Ban moved to appoint Mauritanian diplomat Ismail Ould Cheikh Ahmed to be his new representative.Ban informed the Gulf envoys of his choice but the ambassadors did not specify whether they would accept the mediation, which has taken on a new urgency as the death toll climbs."We have not presented any reaction yet. It is being studied in the capitals and we will have a reaction as quickly as possible," said Mouallimi.Saudi-led air strikes on a missile depot in Yemen's rebel-held capital Monday sparked explosions that killed at least 28 people and wounded nearly 300, flattening houses and shaking faraway neighborhoods.Saudi Arabia launched the air war on March 26 to roll back an advance by the Iranian-backed Huthi rebels, who forced President Abedrabbo Mansour Hadi to flee into exile in Riyadh.Iran last week presented a peace plan for Yemen that called for a ceasefire and immediate end to "all foreign military attacks," the urgent delivery of humanitarian aid and a return to talks on forming a national unity government.