JUBA, South Sudan — A tension-filled showdown in the middle of a market town between rebels and South Sudan's military led to the deaths of four civilians and some 2,000 people seeking refuge with the UN, officials said Monday. The fighting took place Sunday in Pibor, where government forces have been trying to stamp out a rebellion led by David Yau Yau, a former colonel in South Sudan's military. Violence began when James Kuburin, a former commander for Yau Yau who has joined the government, tried to enter Pibor's market, said Beko Konyi, a spokesman for the Pibor County commissioner. Military police refused to allow Kuburin to enter, leading to an argument that resulted in a grenade going off, killing one military policeman, Konyi said. A second government official said that members of the military — the SPLA — “retaliated” for the death by opening fire, killing three women and one man. The official said he was not allowed to be identified. Konyi also said four civilians were killed. Col. Philip Aguer, a military spokesman, denied that SPLA forces started the fighting. He said one member of the military was killed. Kouider Zerrouk, a UN spokesman, said some 2,000 civilians had taken refuge at a UN base in Pibor. Zerrouk described the situation as calm but tense. Sunday's violence was the latest of several incidents in which the SPLA has been implicated in violence against civilians. — AP