In a thrust reverser for an aircraft propulsion unit, the thrust reverser includes an internal fixed structure, a mobile cowl and blocking flaps. The thrust reverser also includes a first actuation mechanism that is configured to move the mobile cowl between a closing position and an opening position so as to cause the blocking flaps to move respectively between a retracted position and a deployed position, thus causing the thrust reverser to pass respectively between a full-thrust configuration and a thrust-reversal configuration. The thrust reverser also includes a second actuation mechanism that is configured to move the blocking flaps between the retracted position and a partially deployed position when the mobile cowl is in the closing position, so as to cause the thrust reverser to pass respectively between the full-thrust configuration and a reduced-thrust configuration.