The German government wants more detailed concepts in the next week from the two rival groups interested in investing in Opel, economy minister Karl-Theodor zu Guttenberg was cited as saying today (14 May).

Berlin wanted Opel assets placed with a trustee in the event that GM filed for bankruptcy before a deal with investors had been concluded, Guttenberg told Reuters after meeting top government officials on the automaker's future.

He had said earlier there was interest in the General Motors Europe unit from investors other than Fiat and Magna, but that the interest of one financial investor had waned.

"We have these two. As to a third one who has made himself known, here the euphoria seems to decline," he told Reuters before the meeting.

He also said the government did not know what Opel's financing needs would be.