Euronext has put no value on its planned offer

Euronext said a merger with the LSE would lead to annual savings of around 203m euros (�138m; $259m).

A unitary, single-tier board would be created and a dual stock market listing would be sought in London and Paris.

The LSE has already rejected a �1.3bn bid from Deutsche Boerse, saying it undervalues the group.

Rivals

Euronext is reported to have facilities in place to fund a �1.4bn cash bid.

The company, which was founded in September 2000 through the merger of the Amsterdam, Brussels and Paris exchanges, also runs the London-based international derivatives market Liffe.

Deutsche Boerse has vowed to cut user costs and pledged to retain the LSE's structure and regulation. But in recent weeks, it has been forced to move to calm mounting concerns among its own shareholders and German authorities.

A deal with either bidder would create the biggest stock market operator in Europe and the second-biggest in the world after the New York Stock Exchange.