NEW : Yemeni official : At least 60 soldiers are killed in the fighting . Fierce clashes erupt as the government fights back . Militants are close to taking over a strategically important base , officials fear . The militants have been using civilians and fighters from other groups for cover.
NEW : Yemeni official : At least 60 soldiers are killed in the fighting . Fierce clashes erupt as the government fights back . Militants are close to taking over a strategically important base , officials fear . Ansar al-Sharia fighters control important roads , residents say .