German Economy Minister Karl-Theodor zu Guttenberg said on Saturday he was talking to potential investors in troubled German carmaker Opel, rejecting a media report saying there was not yet any serious bidder.

I can only repeat: Talks are being held with serious and less serious interested parties, Guttenberg told reporters at an event held by his Christian Social Union (CSU) party in Erlangen, Bavaria state.

But he added that the interest of potential investors was crucially tied the quality of the rescue plan of Opel parent General Motors .

The Spiegel news magazine in a report circulated ahead of publication on Monday said there were not yet any investors in sight, citing Berlin officials who had been briefed by the economy ministry shortly after the minister's trip to the U.S.

Guttenberg met GM Chief Executive Rick Wagoner in the U.S. on Monday. Both said it was essential for GM to find a private investor in Opel to lessen burdens on German taxpayers.

The Berlin ministry on Saturday declined to comment on the Spiegel report.

Guttenberg declined to specify what kind of possible state support measures might be extended to Opel. Opel needs 3.3 billion euros (4.5 billion dollars) in aid either through state loans or guarantees to ensure its survival during the ongoing crisis.

Labour minister Olaf Scholz, of the Social Democratic party, in interview with the Bild am Sonntag newspaper, which was due to appear in print on Sunday, said even the state taking a stake in Opel should not be taboo.

Referring to the demands made by Scholz, Guttenberg said, What must not happen in any case is that money is spent before a sustainable basis (for Opel) has been created. That would be total nonsense.

Opel chief executive Hans Demant told news magazine Wirtschaftswoche that Opel might become profitable after one or two years of aid.

After such a transition time, Opel will post clear profits again with which we would want to repay the credits, he said in an interview in the magazine's March 23 edition.

(Reporting by Anna Holzer)