We compute the exact effective string vacuum backgrounds of the level k=81/19 SU(2,1)/U(1) coset model. A compact SU(2) isometry present in this seven-dimensional solution allows one to interpret it after compactification as a four-dimensional non-Abelian SU(2) charged instanton with a singular submanifold and an SO(3)×U(1) isometry. The semiclassical backgrounds, solutions of the type II strings, present similar characteristics.Facultad de Ciencias Exactas