General Motors has said it was readying a plan to restructure Opel and could pay off debt due this month as German workers went on strike to protest the automakers decision to keep the European unit.

Thousands of auto workers put down tools at German factories, saying GM had betrayed their interests by reversing a decision to sell a majority stake in Opel to a Russian-backed consortium led by Magna International, Reuters reported.

German chancellor, Angela Merkel, angry at being kept out of the loop, had spoken with US president Obama and had been told he had nothing to do with GM's decision, announced hours after Merkel addressed Congress.

"The chancellor made clear that the German government would urge General Motors to present a new plan as quickly as possible and to repay bridge financing by the end of November," a government spokesman said of the phone call in a statement.

Hesse state premier Roland Koch, one of the biggest advocates of Magna's bid, told rallying workers at Opel headquarters on Thursday that he would fight for the firm.

"We want Opel to continue to exist," he said, warning GM not to "maximise profits by taking German workers hostage."

GM chief executive Fritz Henderson told reporters in Detroit he was confident that GM could find the EUR3bn in financing needed to keep and restructure Opel.

He said details of job cuts and plant closures would be presented soon to Germany and other European governments as part of a restructuring plan.

Opel has the liquidity it needs to pay off the EUR900m remaining on a bridge loan from the German government.

At the same time, GM can find ways to provide financing to Opel from its US operations even after a restructuring funded by US taxpayers that had placed some initial restrictions on the automaker's ability to shift funds to its overseas units, Reuters noted.

"We will be very shortly presenting our plan," Henderson said. "We feel confident that the plan will be financeable."

Henderson said GM could provide liquidity to Opel by reducing the royalties that the European unit would otherwise pay to headquarters.

The terms of GM's exit from bankruptcy in the United States after taking $50bn in US government financing also allow GM to send funding directly to Opel if needed, he said.

"We are able to run a global business. We certainly need to be prudent about it. We need to be careful about it but we can run a global business," Henderson said.

Henderson acknowledged that the automaker had "work to do to repair" its relations with the European unions.

British business secretary Peter Mandelson was quoted as saying GM's decision had created uncertainty but he also said the decision could benefit European taxpayers, especially in Britain, Germany and Spain, and that workers at GM's Vauxhall unit in Britain would prefer to keep the same management.

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