Mitsubishi Heavy Industries Ltd. and Siemens AG have improved their offer for Alstom SA on Friday, raising the stakes in the takeover battle with General Electric Co. for the French maker of high-speed trains and power equipment.

Siemens and Mitsubishi Heavy raised the cash component for Alstom by €1.2 billion ($1.63 billion) to €8.2 billion, while the valuation of Alstom's energy assets was increased by €400 million to €14.6 billion, according to a statement sent Friday by Munich-based Siemens.

The group decided to rework its proposal after discussions with its partners to take complexity out of its bid, Siemens said. GE has also improved its offer for Alstom, as the U.S. conglomerate seeks to clinch what would be its biggest purchase yet.