U.S. carmaker General Motors was close to signing a deal to sell a 55 percent stake in its European arm Opel to Canada's Magna Thursday as talks continued with unions over job cuts.

Sources in Germany, home to around half of Opel's 50,000 staff, said the deal could be signed Thursday or Friday.

The deal, set to close by the end of next month, caps weeks of negotiations by the companies and Opel labor leaders, but still awaits details on financing, including 4.5 billion euros ($6.7 billion) in aid being sought from states with Opel plants.

Opel's 50,000 staff are supposed to get a 10 percent stake in the new company in return for cost concessions, while GM will keep a 35 percent stake.

GM decided last month to sell a majority stake to Magna and its Russian partner Sberbank.

Countries with Opel plants have fought to save jobs and avoid plant closures amid promises of billions in state aid.

Talks with unions were continuing in Spain after a union representing workers at Vauxhall, Opel's British sister brand which employs 5,500 people, reached an agreement with Magna earlier in the week.

Magna agreed, among other concessions, not to implement enforced redundancies.

In Belgium, unions agreed to 20.2 million euros of cost savings at the Antwerp plant after Magna pledged to look into keeping the plant open. The facility had been seen as a top candidate for closure.

Poland's economy ministry declined to confirm a radio report saying the government would award 450 million euros in aid.

Poland plans to provide assistance whose amount will depend on the requests and needs of the New Opel in Gliwice, a spokeswoman for Poland's economy ministry said.

The Opel plant in Gliwice builds Zafira and Astra models.

In Spain Opel's prospective new owner Magna offered on Wednesday to return 72 percent of production of the new Opel Corsa to its Spanish plant in 2013.

Until then, production will drop to 70 percent in favor of Germany, the Canadian car parts manufacturer said during a meeting with the regional Aragon government and union leaders in Zaragoza, northern Spain, home to the Opel factory which employs around 7,500 workers.

Magna's latest offer guarantees the Zaragoza plant's capacity with two operating lines of 478,000 vehicles. That's progress, but we're going to continue negotiating today and tomorrow, said Arturo Aliaga, industry counselor for Aragon.

An official at the Comisiones Obreras union said: This is step forward, but we're still waiting for more.

The meeting followed a failed attempt Tuesday in Madrid to reach an agreement over jobs at the Opel car factory in Zaragoza.

The Opel plant at Figueruelas employs 7,500 and Magna had proposed cutting between 1,300 to 1,650 jobs there.

Magna's initial restructuring plans for Opel, which involve laying off more than 10,500 workers in Europe, have run into stiff opposition from European governments.

Magna and Sberbank have vowed to inject 500 million euros into the car maker, aiming to use it to make a push into the Russian market.

The European Commission is keeping a close eye on the transaction to ensure state aid is not misused for political purposes.

(Additional Reporting by Chris Borowski, Judy MacInnes, Christiaan Hetzner and Phil Blenkinsop; Writing by Helen Massy-Beresford; Editing by David Holmes)

($1=.6710 Euro)