The results of molecular dynamics simulations for a soft sphere model of highly asymmetric electrolyte solutions containing macroions and counterions are presented. The macroions carry a negative charge of 12 or 24 elementary charges and the solutions contain monovalent, divalent or trivalent (z(c) = +1, +2, or +3) counterions. The size ratio between macroion and counterion was chosen to be about 5:1 and 7:1. From analysis of both static and dynamic properties we propose a mechanism for the observed formation of clusters between equally charged macroions in these solutions.