JUBA, Sudan (Reuters) - At least 20 people died in a shootout between Sudanese soldiers in a southern town, the military said, warning there was a risk of more clashes as the country divided its forces before the south becomes independent. Fighting with mortars and heavy machineguns broke out in Malakal Thursday and again Friday when part of a military unit refused to redeploy with its weapons to the northpart of a separation of forces before the secession of south Sudan. An overwhelming majority of people from the oil-producing south voted to split from the north in a referendum in January, according to preliminary results released this week. The referendum was promised in a 2005 peace deal that ended a decades-long civil war between north and south that also set southern tribe against southern tribe, in internal conflicts that have left deep scars.