"Opel should have a greater independence and autonomy in the future, but it should also not stand isolated," Magna's head of Europe, Siegfried Wolf, told Bild am Sonntag.

GM changed its mind last week and decided against Opel's sale after half a year of protracted negotiations complicated by government involvement.

The reversal shocked and infuriated unions and politicians in Germany, as well as the Kremlin, which had hoped the deal would help modernize its obsolete auto industry.

"GM must now smooth things out and win back trust. That requires a lot of sensitivity and tact," Wolf said.

Carl-Peter Forster, the head of GM Europe, left the company on Friday after criticising the decision of his own board and told the Bild am Sonntag in comments made prior to his departure that he didn't believe the directors knew what they were doing.

"A sudden shift like this is scarcely comprehensible. I do not find the process in any way OK. I would have wished for a completely different result," he said.

Rival German carmaker Volkswagen's chief executive, Martin Winterkorn, who repeatedly criticised political involvement in the rescue of Opel, said in the paper that he found GM's decision "regrettable, to be totally honest."

Separately, Opel's labour leader Klaus Franz said in the same edition of the Bild am Sonntag that Opel now needed fresh management.

"We need a new Opel CEO from outside the company. He must be a European, with team spirit and petrol in his blood. He must be able to speak languages other than just German," Franz said.

German Economics Minister Rainer Bruederle of the liberal Free Democrats reaffirmed Berlin's stance in the newspaper that the six-month 1.5 billion euro ($2.23 billion) emergency loan for Opel had to be paid back by the end of November with interest.

Meanwhile a GM executive set to become Opel's chairman, was quoted as saying on Sunday that the U.S. company would probably stick to a plan to cut costs at Opel by 30 percent.

"The restructuring plan developed at the end of last year is still the basis for a profitable business model. The plan foresees a 30 percent cut in structural costs," Bob Lutz told the Swiss newspaper Sonntag.

(Reporting by Christiaan Hetzner; Editing by Greg Mahlich)