Miabek Lang, the commissioner of Pariang County in South Sudan's Unity State said the planes dropped bombs Thursday in an area called Yida. He said 12 were killed but that the toll could rise.
Jonathan Hutson, a spokesman for the U.S. advocacy group the Enough Project, said aid workers inside the Yida refugee camp told Enough at least one bomb landed in the camp, and three or four fell outside it. Hutson said at least 15,000 refugees who fled violence in Sudan are living in the camp.
South Sudan become independent from Sudan in July, but violence has flared along the disputed border.