The minority investment, said IAG on Thursday (April 12), was made with a view to initiating discussions with Norwegian, including the possibility of a full offer.
IAG has, however, confirmed no such talks have yet taken place.
67.5% of shares in Norwegian are currently available on the open market.
In a statement, IAG said: "IAG considers Norwegian to be an attractive investment and has acquired a 4.61 per cent ownership position in the airline (minority investment).
"The minority investment is intended to establish a position from which to initiate discussions with Norwegian, including the possibility of a full offer for Norwegian.
