NEW : Yemeni militants kill troops , civilians in southern U.S. . If not , he should step aside and not stall the revolution . '' Fiercest clashes in Taiz since demonstrations began , witnesses say . A Yemen official says Islamic President Tawakkul Karman is `` severely hurt '' Opposition leaders express cautious support for the vice president .
NEW : Yemeni militants kill troops , civilians in southern U.S. . Fiercest clashes in Taiz since demonstrations began , witnesses say . A Yemen official says Islamic President Tawakkul Karman is `` severely hurt '' Opposition leaders express cautious support for the vice president .