The French state has enough cash available from previous share sales to fund the purchase of a 20 percent stake in Alstom (ALSO.PA), Economy Minister Arnaud Montebourg said on Tuesday. The French state secured an option to buy 20 percent of Alstom from its current top shareholder Bouygues (BOUY.PA) on Sunday, clearing the way for an agreed tie-up between Alstom and General Electric (GE.N).