We give a formula for the q-characters of arbitrary highest-weight integrable
modules of sl_{r+1} as a linear combination of the fermionic q-characters of
special fusion products of integrable modules. The coefficients in the sum are
entries of the inverse matrix of generalized Kostka polynomials, which are in
Z[q^{-1}]. In this paper we prove the relation between the character of the
Feigin-Loktev graded tensor product and the generalized Kostka polynomial. We
also prove the fermionic formula for the q-characters of the (unrestricted)
fusion products of rectangular highest-weight integrable g-modules.