Spyker Cars said on Tuesday its talks with General Motors over buying its ailing Swedish carmaking unit Saab must end soon, as swirling speculation about a last-ditch deal sent its shares to 12-month highs.

Hopes of a Saab deal were boosted when General Motors said it would hold a press conference later on Monday to provide a business update, although that could be linked instead to the announcement of a permanent GM chief executive.

General Motors said in a statement that Chief Executive Ed Whitacre will host a press conference in Detroit at 1630 GMT (1130 EST) to provide updates on GM business activities. CNBC reported that GM would name acting chief Whitacre its permanent CEO.

Spyker Cars shares jumped in Amsterdam trading, rising 70 percent to 3.65 euros by 1417 GMT.

Spyker said only that talks with GM were still ongoing.

Spyker confirms that talks are ongoing, the outcome of which is still uncertain. As Saab is currently in liquidation talks must end soon, Spyker Cars said in a statement.

A Swedish Television program had earlier reported, without citing sources, that Spyker was set to announce the purchase of Saab at a Monday press conference and that Sweden has agreed to guarantee loans for the deal from the European Investment Bank.

The report also said Swedish officials were to hold an early-afternoon meeting to discuss the loan guarantees. A Swedish government spokesman said the government took no decisions regarding Saab at that meeting.

Saab Automobile declined to comment on the report, while a spokesman for General Motors in Europe declined to comment.

Lars Carlstrom, the spokesman for rival bidder Genii Capital, said there was still a chance that the deal could be derailed, but expected an announcement later on Monday.

As long as they have not signed there is a chance (of the sale not happening) yet it's most likely we will see an outcome of this today, he told Reuters.

General Motors announced on December 18 it was winding down the 60-year-old Swedish carmaker following the failure of sale negotiations with prospective buyer Koenigsegg.

Two wind-down supervisors took control of Saab earlier this month, but GM said it was continuing to evaluate offers during the wind-down process after Spyker and other parties submitted updated bids for the loss-making brand.

Spyker has been in negotiations with GM over the weekend in Stockholm. Carlstrom said Spyker was no longer relying on financing from the Russian Antonov family, one of its shareholders.

Antonov will be taken out of the deal through a requirement from the U.S. government, he said.

(Editing by Rupert Winchester)

(Reporting by Stockholm and Amsterdam newsrooms)