CAIRO — Iran-backed Houthi rebels struck Yemeni government forces with ballistic missiles on Monday, killing at least 53 soldiers at a military camp in one of the deadliest attacks since a resurgence in fighting this summer, Yemeni military officials said. The attack wounded an additional 200 recruits at the military camp in the southern province of Shabwa, the provincial government there said. The rebels acknowledged targeting the camp. The fighting between the Houthis and Yemen’s Saudi-backed government forces is a widening front in the Iran war that began in February. The escalation shattered a 2022 ceasefire deal that largely stopped fighting in Yemen’s civil war. The Houthis have put their growing military capabilities on display on multiple fronts in recent weeks, repeatedly striking Saudi Arabia’s main international airport hundreds of miles (kilometers) away and seizing territory inside Yemen near a key shipping chokepoint. In a sign that the Houthi attacks are unsettling Saudi society, the kingdom on Monday canceled a global investment conference scheduled for next week