South Sudanese authorities are holding up United Nations fuel tankers over a tax dispute, jeopardising the delivery of millions of dollars of aid during a humanitarian crisis, the U.N. mission there said. The trucks were held up at depots and the Ugandan border on Wednesday despite assurances from the minister of humanitarian affairs a day earlier that a new tax on trucks carrying fuel and other supplies did not apply to U.N. humanitarian operations, a spokesperson for the mission said. Minister of Humanitarian Affairs Albino Akok Atak and Information Minister Michael Makuei were not immediately available for comment.