Mitsubishi Heavy Industries is eyeing a minority stake in France's Alstom, according to an AFP source, after a Japanese media report said it would team up with German giant Siemens to offer $10 billion for certain energy assets.

The firm has prepared an alternative plan to buy shares in the French "national jewel", seeking a tie-up similar to Renault's stake in number-two Japanese car maker Nissan.

"Details of the offer are being finalised and are likely to be disclosed on Monday," the source added.

The comments followed a report about the possible tie-up in French newspaper Le Figaro.

The story appeared to be at odds with a report by Japan's leading Nikkei business daily which said that Mitsubishi, Hitachi and Siemens were teaming up to buy Alstom's gas and steam turbine business.

The firms have said they are considering a joint proposal for "certain assets" of the French company but offered no details - a move that could scuttle General Electric's $17 billion offer for Alstom's wider energy group.

A Mitsubishi spokesman said: "We cannot provide details about what we've announced already - that together with Siemens we are evaluating a potential proposal for Alstom."

The French president's office said it is pushing for improved job and energy security guarantees from two bidders for Alstom's power-generation.

Alstom is one of France's biggest private sector employers with about 18,000 staff nationwide, but depends heavily on French government contracts.

GE's $17bn bid has run into political opposition in France, as the government views Alstom as a firm of national strategic importance and is concerned about safeguarding jobs as it battles record unemployment and declining industrial competitiveness.

Seeking to allay any fears about possible layoffs arising from a deal, GE promised late May to create 1,000 jobs in France.