RIYADH, CAIRO: New fighting has erupted in northern Yemen as support for Iran-backed Houthi militias in their heartland crumbles. Thousands of civilians caught in clashes between warring factions are trapped in the impoverished Hajjah governorate. The number of people displaced has doubled in the past six months, with over 5,300 families fleeing in the past weeks, according to the UN Office for the Coordination of Humanitarian Affairs. The Houthis imposed tight control over Hajjah’s mountainous district of Kushar after powerful local tribesmen took up arms against them. The Houthis shelled the district — home to 100,000 people — and killed and wounded scores of civilians. Thousands were displaced. As the Houthi siege strangled the area, the Saudi-led coalition airdropped food and medicine to the tribes. “Ongoing fighting in the north of Hajjah is creating an extremely concerning situation for the population,” said the medical charity Medecins Sans Frontieres, which is operating in the region. The district’s tribes remained neutral in Yemen’s civil war after a 2012 deal with the Houthis. But after the Houthis tried to use the district to send weapons and reinforcements to the front lines, the deal collapsed. Ali Argash, a Yemeni university professor who grew up in Kushar, said that for the past two months mediation between tribal leaders and Houthis failed to prevent a conflict. “We were searching for peace and told them, you are the de facto authority, tell us what you want and we will do it,” he said. “We tried to avoid the war but we were forced into it.” The fighting underscores the fragmentation of the Houthis’ support base in northern Yemen, where they have mostly been in control since the start of the conflict. In Al-Jawf province, Yemen’s National Army killed 13 Houthi militants while trying to infiltrate national posts in Al-Motoon discrict, according to a statement on Yemen’s national army website “September net.” Other Houthis were injured when coalition planes bombarded their vehicles in the district.