[en] A general detailed analysis for the nonlinear generation of localized fields, due to the existence of a strong pump field inside the non-uniform plasma, has been considered. We have taken into account the effects of relativistic and non-local nonlinearities on the structure of plasma resonance region. The nonlinear Schroedinger equation describing the localized fields is investigated. Besides, the generalized dispersion relation is obtained to study the modulational instabilities in different cases. (author)