In order to design an augmented reality system applied to liver punctures, we devised previously the algorithms that permit to obtain quickly an accurate patient to model registration. In this article we tackle the interface design of the system. The main constraints are the speed and accuracy with which an expert can position correctly a needle into a predefined target. Moreover, to ensure the system safety, the interface has to inform the expert when a registration failure occurs. We present here our interface that allows to fulfill the intervention requirements, by combining the two classical concepts: Augmented Reality and Augmented Virtuality. A validation, on an abdominal phantom, showed evidence that an expert can reach very accurately and quickly the predefined targets inside the phantom.