German conglomerate Siemens and Japan's Mitsubishi Heavy Industries on Wednesday said they had joined forces for a possible bid for some assets of France's Alstom.

Siemens and Mitsubishi said in a joint statement they would decide on a proposal to Alstom's board of directors by Monday next week.

"We firmly believe that we can substantially contribute to a partnership solution for Alstom which will create value for all parties involved, including the country of France," Mitsubishi Heavy Chief Executive Shunishi Miyanaga said in the statement.

Earlier on Wednesday, a source close to Siemens told Reuters the two companies were talking about a possible joint bid for Alstom's power activities, which are already the target of a $17 billion offer from U.S. company General Electric Co..

The source confirmed a report by Bloomberg which said that one option being discussed was for Mitsubishi to bid for Alstom's steam and grid businesses while Siemens would acquire its gas turbine operations. The report said the German firm would transfer its train assets to Alstom as part of any deal.