  We obtain extremal stationary solutions that generalize the
Israel-Wilson-Perj\'es class for the low-energy limit of heterotic string
theory with n>=3 U(1) gauge fields toroidally compactified from five to three
dimensions. A dyonic solution is obtained using the matrix Ernst potential
(MEP) formulation and expressed in terms of a single real 3X3-matrix harmonic
function. By studying the asymptotic behaviour of the field configurations we
define the physical charges of the field system. The extremality condition
makes the charges to saturate the Bogomol'nyi-Prasad-Sommerfield (BPS) bound.
