"Siemens has submitted a letter to the board of Alstom to signal its willingness to discuss future strategic opportunities," the company said in a statement, adding that it would make no further comment at this time.
Siemens made the announcement just as Alstom is being pursued by US giant General Electric, and a day after a source close to the matter said the German company was planning a rival bid.
GE's chief executive Jeffrey Immelt is due in Paris later Sunday for talks with senior French government officials about its potential offer for Alstom, a highly politically sensitive symbol of engineering prowess in France and a key exporter.
The company is facing a financial crunch and its shares have dropped sharply in the last year.
Although the French state has not held a stake in Alstom since 2006, Immelt is due to hold talks with Economy Minister Arnaud Montebourg and Prime Minister Manuel Valls on Sunday, according to several sources.
France's government wants to obtain guarantees on "jobs, the location of activities and energy independence", said President Francois Hollande's office.
When Alstom was on the brink of collapse in 2003-2004, the French state strongly opposed a takeover by Siemens.
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