A locking assembly for securing a rod in a receiving part of a bone anchoring device includes a first locking element having a first end and a second end and a longitudinal axis of rotation and an outer surface provided with an external thread, a coaxial bore passing entirely through said first locking element and an internal thread provided at said bore, a second locking element having a: longitudinal axis of rotation and an outer surface with an external thread cooperating with the internal thread of said first locking element. The first locking element has a recess between the first end and the second end, that defines a circumferentially closed wall portion. The interior of the wall portion has a longitudinally extending structure for engagement with a tool. Furthermore, a tool is provided which has sections which can be independently engaged with the first and second locking element, respectively.