President Obama spoke today with President Kiir to urge him to build on the recent achievements of the nationality and citizenship agreements initialed by South Sudan and Sudan, and to express hope that the two countries' heads of state will meet soon at a summit, as they had previously agreed. President Obama also expressed concern about the growing tensions between South Sudan and Sudan, especially the violent clashes along their shared border and renewed fighting in Southern Kordofan State. President Obama underscored the importance of avoiding unilateral actions, and asked President Kiir to ensure that South Sudan's military exercises maximum restraint and is not involved in or supporting fighting along the border, particularly in Southern Kordofan. The President further emphasized the importance of South Sudan and Sudan reaching an agreement on oil. President Obama welcomed President Kiir's commitment to moving forward with a summit and to finding peaceful solutions for Sudan and South Sudan.
Barack Obama, Readout of the President's Call with President Kiir Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/303169