Fragmentation of 158 AGeV Pb nucleus after the collision with Pb and plastic targets has been studied using several lead-emulsion chambers irradiated in SPS at CERN. It was found that more than 50% of Pb+Pb interactions at 158 AGeV are of electromagnetic origin. The distributions of the number of fragments are target dependent while their charges and the shapes of their angular distributions are independent of the target mass. For a given energy transferred to the spectator part of the nucleus the mean values of the number of fragments and their charges as well as angular distributions are the same for light and heavy targets, except for the most central collisions.

PACS numbers: 25.75.+r, 29.40.Rg