Niki, a unit of Air Berlin (>> Air Berlin Plc), filed for insolvency on Wednesday.

Zeitfracht and maintenance group Nayak are jointly interested in some assets, including Niki crews, in order to expand Zeitfracht's newly-bought subsidiary WDL Aviation, the spokesman said.

They were also interested in Niki Technik, he said.

This adds to the list of interested parties.

Former motor racing driver Niki Lauda, who founded the Niki airline in 2003, British holiday group Thomas Cook (>> Thomas Cook Group) and Irish low cost carrier Ryanair (>> Ryanair Holdings plc) have also expressed an interest in its assets.

Zeitfracht and Nayak have already bought Air Berlin's cargo marketing platform Leisure Cargo and maintenance units.

Niki's insolvency came after Germany's Lufthansa (>> Lufthansa Group) scrapped plans to buy Niki, grounding the airline's fleet and stranding thousands of passengers.

Administrators for parent company Air Berlin have since been working to find a new buyer for Niki's assets, which include valuable take off and landing slots in airports such as Duesseldorf, Munich and Vienna.

They are under pressure to clinch a deal before Niki loses its airport slots, which could be in a matter of days, depending on the outcome of talks between the Austrian transport ministry and the airport coordinator.

Lufthansa abandoned plans to buy Niki due to the European Commission's competition concerns.

(Reporting by Kerstin Doerr, Writing by Victoria Bryan and Vera Eckert; Editing by Mark Potter)