Sporadic tribal clashes between Arabs and non-Arabs continued Tuesday in Sudan’s West Darfur province, as the death toll climbed to at least two dozen people, some of them burned to death, according to a local aid group working in the area. Some of the 24 dead were children, said Adam Regal, a spokesman for a local organization that helps run refugee camps in the area. The clashes, which erupted over the weekend, pose a challenge to efforts by Sudan’s transitional government to end decadeslong rebellions in areas like Darfur.