A system and method for ensuring safe and tolerable insertion of a needle into a subject's body according to a preplanned or continuously monitored sequence of insertion steps. The system comprises a gripping device for gripping the needle in order to perform robotic insertion steps, yet for releasing the grip between such insertion steps, until the next insertion step is initiated. Thereby, the robot has full control of the needle during insertion steps, but does not constrain the needle between insertions, such that movement of the subject can cause neither damage nor discomfort. The gripping and insertion steps may be coordinated to keep in synchronization with the subject's breathing cycles, such that the insertion steps may be performed in the same segment of each cycle of motion of the subject's chest. The gripper can either fully disconnect from the needle, or can partially disconnect but constrain motion within limits.