KHARTOUM, April 1 (Reuters) - At least 40 people have been killed in tribal clashes in Sudan's troubled Darfur region, aid groups said on Sunday. Tribal fighting is becoming a growing concern for U.N. officials, who say the clashes have killed more people than the conflict between government forces and rebels, with hundreds dead in the past few months. Aid groups said at least 23 people were wounded in the clashes on Saturday in southern Darfur near Diyala.
