U.S. and British diplomats urged Houthi forces to end an offensive in northern Yemen on Sunday after at least 17 people were killed in an explosion which the Saudi-backed government blamed on a Houthi missile strike. The Houthi group, which ousted the government from the capital, Sanaa, in late 2014 later said it had only struck a military camp in Marib City on Saturday and welcomed an independent investigation into the incident. Among those killed in Saturday"s explosion near a petrol station in Marib City was a five-year-old girl who was charred beyond recognition. Reuters TV footage showed the partially covered bodies of the child and a man, who the interior ministry said was her father, lying in a military hospital. Medical sources at the hospital told Reuters on Sunday that the death toll had risen to 21 after authorities said it was 17. The internationally recognised Yemeni government, which has been battling the Houthi movement for over six years, said the blast - which wrecked the petrol station and gutted cars - was caused by a Houthi missile. read more Marib has become the focal point of the war since the Houthis launched an offensive to seize the gas-rich region, the government"s last stronghold in northern Yemen. read more "This inhuman violence must end," Cathy Westley, charge d"affaires at the U.S. embassy, said in a statement. The British ambassador to Yemen, Michael Aron, said on Twitter that serious engagement by the Houthis with U.N. efforts to secure a nationwide ceasefire would "prevent such tragic losses". Yemen has been mired in violence since a Saudi Arabian-led military coalition intervened in March 2015 against the Houthis, who say they are fighting a corrupt system and foreign aggression. The conflict has killed tens of thousands of people, including in coalition air strikes, and caused what the United Nations says is the world"s largest humanitarian crisis with 80% of the population reliant on aid.