Juba, Muharram 17, 1437, Oct 30, 2015, SPA -- South Sudanese rebels seized a barge on the Nile River and are holding 12 contractors working for the United Nations, dpa quoted a UN spokesman in New York as saying Thursday. The barge, operated by the UN Mission in South Sudan (UNMISS), was in Kaka north of Malakal when it was stopped on Monday by more than 100 heavily armed men affiliated with a rebel group aligned with the country's main opposition party, the spokesman said. "Earlier today all 20 of the detained UNMISS peacekeepers were extracted by helicopter from Kaka to Malakal," the spokesman said. "The opposition has however kept in Kaka all 12 of the UNMISS contractors, the barge and some of the weaponry and equipment belonging to UNMISS peacekeepers." The mission is "extremely concerned" that the national crew of the barge has not been released and that the barge has not been returned to the UN, the spokesman said. "The mission demands that the UNMISS national contractors be released immediately, unharmed and unhurt," he said. A rebel spokesman told dpa earlier that barges traveling from Juba to Upper Nile State were stopped because they were carrying flags that "look confusing." "We are going to release the barges after confirmation from the UN," Colonel William Gatjiat said. The Sudan Tribune reported that the barge had already been released on the instructions of rebel leader Riek Machar. -- SPA 03:10 LOCAL TIME 00:10 GMT www.spa.gov.sa/w