THE head of Libya's National Oil Corp (NOC) rejected the prime minister's authority to sack him, raising the prospect of an open struggle for control of the state energy producer. In a furious televised speech, Mustafa Sanalla said Prime Minister Abdulhamid al-Dbeibah's mandate to govern had expired and warned him not to touch NOC. An armed force deployed outside the NOC building later in the day, three witnesses said. One of them said the force was aligned with Dbeibah. A spokesperson for the Government of National Unity, which is headed by Dbeibah, was not immediately available for comment. Libya's messy…