Russia's Sberbank and GAZ Group are joining Magna in talks to buy a controlling stake in General Motors' Opel unit, Russian media reported on Tuesday.

Thuringia state economic minister Juergen Reinholz  reportedly confirmed the two companies' entry into a consortium with Magna. Opel has a plant in Eisenach in the eastern state.

GM could give Opel to the consortium in exchange for guarantees to invest at least EUR500m in the struggling division, a source 'close to Magna' told business daily Vedomosti.

While Opel has been widely reported to need EUR3.3bn in state aid from European governments to stay afloat, the Kommersant business daily, citing German officials, said the three companies would need EUR5-7bn to solve Opel's financial problems.

None of the parties would comment.

Magna founder Frank Stronach last week told an Austrian newspaper that his company was  in talks with General Motors and German government officials about possibly taking a minority stake in Opel but stressed there was no assurance that any transaction would result from the talks.

Magna was interested in "helping" Opel, which it supplies, but Stronach added that it was too early to know what role Magna might play.