It said the minister had been shot in the head and chest as he got into his car in the east of the capital.
Witnesses said the incident happened at around 7:50 p.m. (1620 GMT), IRNA said.
"Investigations show that two shots were fired from inside the vehicle," the agency quoted a police official as saying.
"That two shells were found inside the car shows a strong likelihood that the assailant was inside the car and in conversation with Mr Abadi. There was no sign of struggle at the scene of the killing."
(Writing by Kevin Liffey; Editing by Janet Lawrence)