Friction phenomena may strongly deteriorate performance and reliability of force-controlled systems. Although different solutions exist, ensuring accurate and robustly stable friction compensation is still a challenging task due to model inaccuracies and parameter identification issues. This paper proposes a novel friction observer architecture designed to achieve accurate friction compensation in force control applications, without relying on a specific friction model. Since passivity is a fundamental requirement for interaction control, a passivity analysis is reported showing that the proposed solution preserves passivity at the environment, control and friction ports. This implies that the proposed observer can provide a passive friction compensation action for any friction dynamics and can be combined with any passive controller while guaranteeing a stable interaction with any passive environment. The proposed approach is validated through simulation and experimental trials, considering different interacting environments and diverse friction phenomena affecting the actuator dynamics. A main impact of the proposed approach is expected on collaborative and assistive robotics, including active industrial exoskeletons where interaction reliability and transparency are of paramount importance.