Germany's Siemens is working on a formal asset-swap offer for Alstom's power business that could come as early as this week and see France take a stake in a resulting rail-focused French group, sources close to the talks told Reuters.

Alstom is already in talks with U.S. conglomerate General Electric over a 12.35 billion euro ($16.9 billion) bid for its power arm, which it is due to review by June 2. However, under strong political pressure, it has opened its books to Siemens so it can propose its own deal if it wants to.