The Iran-backed Houthis have escalated attacks on the Saudi-backed Yemeni forces, days after the United States moved to delist the rebels as terrorists and stepped up efforts to de-escalate the six-year conflict. Fighting in Yemen's north has left dozens dead and wounded, a government source said, as UN agencies issued stark warnings that 400,000 children risk death this year from lack of food. Yemen's Iran-backed Houthi rebels have resumed an offensive to seize strategic oil-rich Marib, the government's last northern stronghold, the loss of which would be disastrous for the beleaguered leadership. "Dozens of people have been killed and wounded on both sides," a government source told AFP, reporting a Houthi missile fired into Marib's suburbs and air strikes from the Saudi-backed military coalition pounding rebel positions. "Most of the deaths were Houthis hit by air strikes," he added. Yemen is engulfed in a bloody power struggle that erupted in 2014 between its government, supported by Saudi Arabia, and Iran-backed Houthi rebels, who control the capital Sanaa and most of the north. The grinding conflict has claimed tens of thousands of lives and displaced millions, according to international organisations, with close to 80 percent of the 29-million population in need of some form of aid for survival. 'Malign actions and aggression'  The upsurge in violence comes as Washington said it would remove the Houthi rebels from its list of terrorist groups next Tuesday, overturning sanctions put in place by the administration of ex-president Donald Trump. The sanctions had sparked an outcry from aid groups, who said the designation would put them at legal risk and severely hamper efforts. "The revocations are intended to ensure that relevant US policies do not impede assistance to those already suffering what has been called the world's worst humanitarian crisis," US Secretary of State Antony Blinken said Friday. "The United States remains clear-eyed about Ansar Allah's malign actions and aggression," Blinken added, referring to the Houthi movement by its formal name. While the US reset is aimed at restarting the peace process, Blinken said that sanctions on individual Houthi leaders would remain in place.