This paper deals with the problem of combining motion and task assignment for a dual-arm robotic system. Each arm of the system performs independent tasks in a cluttered environment. Robot actions are determined to remove potential obstacles and obtain collision-free paths to grasp the target objects. The approach uses the information provided by the motion planner to build a graph structure in order to represent the obstacles to be removed. The graph is used, first, to decide which is the next motion path to be computed, and, second, to assign the tasks to each arm of the robotic system. The approach has been implemented for a dual-arm robotic system and real experiments are presented in the pape