The German government is examining competing plans to invest in Opel and hopes to decide on financing guarantees by the end of the month, a leading Social Democrat (SPD) politician said on Sunday.

Fiat is eyeing a three-way merger with Chrysler and General Motors' European operations while Magna reportedly is seeking Russian backing to invest in Opel.

"The government is comparing the two concepts in order to make a decision on the required billions of euros in guarantees by the end of May," SPD parliamentary leader Peter Struck told the BZ newspaper, according to Reuters.

SPD is junior partner to chancellor Angela Merkel's conservatives in Berlin's uneasy 'grand coalition', the news agency noted.