Four months before Southern Sudan is scheduled to hold an independence referendum, tensions are already rising in this oil-rich region that sits on the expected future border, with allegations the central government is using violence and ethnic cleansing to sway the vote.Leaders in Sudan's north and south are in a tug-of-war over the central Sudan region of Abyei, home to oil fields worth hundreds of millions of dollars. In conjunction with Southern Sudan's independence referendum scheduled for Jan. 9, Abyei is to vote the same day to decide if it should belong in Sudan's north or in a possible new country in the south.