IAG shares took a hit and descended about one percent so far.
"IAG considers Norwegian to be an attractive investment and has acquired a 4.61 percent ownership position in the airline", said the group that includes British Airways and Ireland's Aer Lingus, as well as Spanish airlines Iberia and Vueling.
'IAG confirms that no such discussions have taken place to date, that it has taken no decision to make an offer at this time and that there is no certainty that any such decision will be made, ' a spokesperson added.
Norwegian is one of the few low-priced airlines to venture into long-haul flights, which has always been the preserve of major carriers, and has been rapidly adding flights.
"Norwegian believes that IAG's interest in the company confirms the sustainability and potential of our business model and global growth", it said.
Fierce competition between two airlines low cost long radio flights is focused on El prat airport in Barcelona. March also saw low-priced subsidiary LEVEL begin a new route from Barcelona to Boston, and in July the airline will start operations from Paris-Orly to Montreal, New York (Newark), Guadeloupe and Martinique.
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In low-priced national and European routes, it is Vueling that rivals Norwegian.
As a result, the stock price of Norwegian surged to over 40 percent on Thursday, after a rough year of decline following stockholders concerns about the profitability, the level of debt and expansion rate of the carrier. In 2017, it recorded net losses of 299 million of Norwegian kroner (30.8 million euros), compared to profit of 1.135 billion of crowns (116.8 million of euros) which it obtained in previous year.
With attempt to take on Norwegian, IAG takes anor step in its vocation since its founding in 2011, with merger between Iberia and British Airways, to become one of protagonists of consolidation of air transport sector.
The firm put its hat in the ring to pick up bust rival Monarch's landing slots at Gatwick.
IAG's Aer Lingus reported a 2.8 percent increase in revenue tonne-kilometers for the first three months of 2018 compared to the same period past year as British Airways reported a 2.0 percent drop and Iberia traffic rose 4.7 percent in the period.