British International Airlines Group (IAG) was in exclusive talks to buy the former subsidiary of insolvent Air Berlin, a source close to the process told the German news agency DPA on Thursday, after Niki's administrator said that one bidder out of four had remained.

"IAG is the last remaining bidder and is still negotiating now," the person was quoted as saying by DPA. Reportedly, IAG had made "the highest bid" in the range of "a double-digit million-euro amount."

German newspaper Bild put the figure at around €40 million ($48 million) without citing sources.

A spokesman for Niki insolvency administrator Lucas Flöther, however, refused to confirm the media reports, saying only that the provisional creditors' committee for Niki "decided to continue sales negotiations for the business operations of the company exclusively with one bidder for now."

With its network of European and North African vacation destinations, Niki declared itself insolvent this month after German carrier Lufthansa withdrew its takeover offer for the airline. Lufthansa abandoned its bid for Niki after the acquisition was rejected by the European Commission on competition grounds. But the EU regulators approved of Lufthansa's takeover of 85 aircraft once belonging to Niki parent Air Berlin.

Last bidder

Founded by former Formula One champion Niki Lauda in 2003, Niki was sold to Air Berlin Group in 2011. By the end of a deadline Thursday last week, six bidders had emerged for the Austrian-based airline.

Five bids were binding, Flöther said in a statement Friday, without providing details. "The bidders are very interested, and I am confident that it will be possible to save large parts of the business and many jobs in Austria and Germany," he added.

Besides the British airline group, they included tour operators TUI, Thomas Cook, Swiss carrier PrivatAir and former Formula One world champion Niki Lauda.

Read more: The changing skies of Europe

Niki Lauda is now quoted as saying on the website of Austrian newspaper Die Presse that he was out of the running. A source said Thomas Cook was also out of the race.

Die Presse also reported that IAG was likely to be the last bidder. IAG and Thomas Cook's Condor subsidiary declined to comment on Thursday. TUI was not immediately available to comment.

The new owner will have to pay Niki's running costs, including salaries for its roughly 1,000 employees in Austria and Germany, from the beginning of January, the administrator said on Wednesday.

uhe/nz (Reuters, dpa)