A long-simmering conflict between Armenia and Azerbaijan over the disputed region of Nagorno-Karabakh flared up on Sunday after both sides fired rockets and artillery, leading to the deaths of at least 30 people in clashes that continued on Monday. It was not immediately clear what sparked the fighting. The latest violence in the conflict, which has run hot and cold since a 1994 ceasefire, has led to fears of a renewed tit-for-tat cycle of border clashes.