A valve actuation mechanism includes a rocker adapted for opening a cylinder valve, via an activation piston movable in a piston chamber of the rocker under action of a fluid pressure raise in the piston chamber, from a first position in which an engine operating function is deactivated to a second position, in which the engine operating function is performed, the rocker including a controlled blocking valve, wherein the control of the blocking, valve between its open state and its blocking state is performed by action of a force exerted by the fluid pressure in the piston chamber on a valve member of the blocking valve which is exposed to the fluid pressure in the piston chamber.