We study the propagation of ultra-high energy cosmic ray nuclei through the background of cosmic microwave and intergalactic infrared photons, using recent re-estimates for the density of the last ones. We perform a detailed Monte Carlo simulation to follow the disintegration histories of nuclei starting as Fe and reaching the Earth from extragalactic sources. We obtain the maximum energies of the arriving nuclear fragments as well as the mass composition as a function of the distance traveled. Cosmic rays with energies in excess of 2 × 10²⁰ eV cannot originate from Fe nuclei produced in sources beyond 10 Mpc.Facultad de Ciencias Exactas