Sihag is an Additional Secretary and Financial Adviser in the Steel Ministry, which governs the Navratna firm, and was first given the additional charge of CMD NMDC in January after its then Chairman Narendra Kothari retired in December 2015.
"In terms of order dated July 13 of Steel Ministry, the additional charge of the post of CMD NMDC is assigned to Sihag for a further period of three months with effect from July 1, 2016," NMDC said in a regulatory filing.
In April, the government had extended Sihag's tenure as CMD of the Public Sector undertaking (PSU) by three months, effective from April 1, 2016.
Government's head hunter Public Enterprises Selection Board (PESB) has so far not been able to find a full-time successor to Kothari.
Earlier, PESB had recommended Gopal Singh for the top post, but sources said the Appointments Committee of the Cabinet has still not given its nod on the same. Singh has been heading Central Coalfields Ltd (CCL) since March 2012.