Niki, a unit of Air Berlin ceased operations late Wednesday after applying to open insolvency proceedings. Following the news, Lufthansa announced that it was no longer interested in buying Niki together with the rest of Air Berlin because of EU competition concerns.

Thousands of European travelers could be left stranded following bankruptcy of Austrian budget carrier Niki. Niki posted a notice on its website saying passengers should contact their tour operator if possible. It said several other airlines have offered to fly passengers back to Germany, Austria and Switzerland for a small fee if they booked directly through Niki.

Niki's founder Niki Lauda, the Austrian former Formula One champion, said Thursday he was potentially interested in acquiring again the airline he sold to Air Berlin in 2011.

Lufthansa has been keeping Niki in the air with around 10 million euros per week, according to Bloomberg News.