US and British envoys to Yemen on Sunday urged Houthi forces to end their offensive in the north of the country after at least 17 people were killed in an explosion that the Saudi-backed government said was caused by a Houthi missile attack.

Among the dead in yesterday's explosion, which occurred near a gas station in the city of Ma'rib, was a five-year-old girl whose body was charred beyond recognition. Footage filmed by Reuters TV showed the partially covered bodies of the girl and a man the Interior Ministry said was her father.

Hospital medical sources told Reuters on Sunday that the death toll had risen to 21, after authorities had earlier said it was 17.

The internationally recognized government, which has been fighting the Houthis for nearly six years, said the explosion, which destroyed the petrol station and charred car bodies, was caused by a Houthi missile.

There was no comment from the Houthi group, which ousted the government from the capital, Sanaa, in 2014.

Marib has become the epicenter of the conflict since the Houthis launched an offensive to seize the gas-rich region and the government's last stronghold in northern Yemen.

"This inhuman conflict must stop," said Kathy Wesley, Chargé d'Affairs at the US Embassy.

Michael Aaron, the British ambassador to Yemen, wrote on Twitter that the Houthis' serious participation in the UN efforts to reach a nationwide ceasefire would "prevent such tragic losses."

Yemen has witnessed violence since a Saudi-led military coalition intervened in March 2015 against the Houthis, who say they are fighting a corrupt regime and foreign aggression.

The conflict has killed tens of thousands of people, including those killed in air strikes, and created what the United Nations calls the world's largest humanitarian crisis, with 80% of the population dependent on aid.