The statement went beyond one Economy Minister Emmanuel Macron made in February, coming from the man in charge of banking and financial industry issues in France and warning of a potential impact on the European economy.

The proposed merger would create a group similar in scale to U.S. exchange ICE, which has taken huge slices of Europe's derivatives markets, and would leave smaller European competitors such as Euronext far behind.

Euronext operates the Paris bourse as well as stock exchanges in Amsterdam, Brussels and Lisbon.

"I want to express the concern of the French government on this tie-up," Sapin said in a statement emailed to Reuters by his spokesman. "We have doubts about the consequences this could have for the financing of the real economy in France and Europe."

"The merger of these two entities will result in a large group which could hold within it a majority of the tools that make our markets function efficiently. That poses a competition problem, and we want to make sure the European Commission gets involved to avoid a situation where a dominant position arises."

Sapin's cabinet colleague Macron had earlier voiced concerns in Brussels about possible competition issues and said France would assess the strategic consequences for Paris's financial centre.

Aware of the risks of being marginalised, Euronext said this month it was on the lookout for tie-ups of its own as it unveiled a new strategic plan.

(Reporting by Michel Rose; Writing by Andrew Callus; Editing by James Regan)

Stocks treated in this article : Deutsche Boerse AG, London Stock Exchange Group Plc, Euronext