BERLIN: Italy's Fiat has improved its offer for General Motors' Opel unit, the German economy minister said on Saturday after a rival Canadian-Russian bid appeared set to win Berlin's seal of approval.

A government spokesman said that Economy Minister Karl-Theodor zu Guttenberg had said in Berlin that Fiat had improved its bid for a stake in the GM unit and had offered more details.

The final decision on Opel, as well as other units of GM's European operations, including Britain's Vauxhall and Sweden's Saab, lies with GM itself and the US government.

But Berlin has a major say as it has promised to sweeten any deal with loan guarantees, and last week it appeared that Canadian auto parts maker Magna International had made a more convincing offer.

Magna is bidding together with Russian tycoon Oleg Deripaska's truck company GAZ and is backed by Russia's biggest lender, the state-run Sberbank. Press reports have said that its bid is preferred by GM.

Brussels-based investment group RHJ International has also made an offer for the struggling General Motors unit, which employs 25,000 people directly.

Fiat wants to combine GM's European and Latin American operations with the bankrupt Chrysler to form the world's second largest automaker behind Japan's Toyota.

According to press reports, Magna and RHJ were expected to ask for five billion euros (seven billion dollars) in guarantees while Fiat was reported to be requesting seven billion euros.