A rigorous modelling of open space problems or matched guided structures including radiation phenomena needs an enormous computational effort. This effort is more important when applying a volumic method that requires the meshing of the entire computational domain and the use of absorbing boundary conditions. In this work we present a hybrid formulation of the frequency-domain TLM method (FDTLM) with an integral field equation. This hybrid method combining the advantages of both numerical methods is applied to model a diffraction problem where an infinite metallic square cylinder is exposed to an incident plane wave. As compared to the standard FDTLM, the hybrid method avoids the use of absorbing boundary condition and, thus, reduces the total computational TLM domain.