On Monday, eastern Libyan armed forces took over the field. But NOC said in a statement it had received no official communication from El Sharara that the field had been secured.
The 315,000 barrels per day oilfield has been closed since state guards and tribesmen asking for funds seized it in December.
The Libyan National Army (LNA) force based in eastern Libya began an offensive in the south last month to fight militants and secure oilfields.
NOC also said a non-fly zone imposed by the LNA for any air traffic without its permission would have to be lifted for workers to be able to fly in and out.
Oil production in Libya, a member of the Organization of the Petroleum Exporting Countries, has been disrupted since conflict broke out in 2011, with protesters and armed groups often targeting oilfields and energy infrastructure.
National production stands at under 1 million barrels a day, well below pre-2011 capacity of 1.6 million bpd.
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