Last month's game at San Siro finished 1-0 in Inter's favour, as Roberto Mancini's side sealed their place in the last 16 by virtue of a 4-3 aggregate scoreline.
In a statement released by UEFA, European football's governing body declared that both clubs had been fined €5,000 for the behaviour of the fans.
The statement also revealed that Celtic had been fined a further €8,000 for the "improper conduct of their team" after Virgil van Dijk was sent off for two bookings in the first half and five other players were cautioned.
Elsewhere, Dynamo Moscow have also been fined €20,000 after their supporters also let off fireworks during the 0-0 draw at Anderlecht in the last 32 first leg tie.
‘I don’t think Liverpool would look at Ollie Watkins, a striker isn’t a pressing issue for them – it’s Arsenal who need one’ Former Reds star explains why his old club don’t need an out-and-out forward this summer
‘He’ll still be playing at 40 at a good level because he’s in such good shape and looks after himself so well. He does everything to be a top professional’: Ex-Liverpool coach insists Mohamed Salah has plenty more miles in the tank
