Iran Air has finally concluded an agreement for up to 40 ATR 72-600 turboprops, originally disclosed more than a year ago.
ATR says that the deal has been "officially signed" and covers 20 firm aircraft and 20 options.
The agreement is part of a broad fleet modernisation by Iran Air which has also included deals for 180 Airbus and Boeing jets.
Iran Air and ATR have yet to disclose the delivery schedule for the turboprops.
But several ATR 72-600s have already been painted in Iran Air colours, and have been parked at Toulouse awaiting delivery to the airline.
These aircraft include an airframe which conducted a demonstration tour in Iran last September.