The referendum was originally planned to be held simultaneously to the 2011 South Sudanese independence referendum on January 9–15, 2011, but was postponed indefinitely due to disagreements over the process.[2][3] Due to the uncertainty, violence erupted in which more than 30 people were killed. As a response the UN deployed extra troops to its UNMIS contingent[4] The impasse on the referendum is due to lack of agreement on who constitutes a "resident of Abyei". The question is whether to include the Messiria tribe, who have historically stayed in the region every year for six months.[5]