The New York Stock Exchange Group yesterday spelled out its determination to use its merger with Euronext to compete head-on with the London Stock Exchange (LSE), which has beaten it in listing international shares in recent years.

It also raised the possibility that a combined NYSE-Euronext could move on to swallow Germany's Deutsche Börse, a rival suitor for Euronext.

In a joint press conference to announce details of their planned merger - largely unchanged from those announced two weeks ago - John Thain, NYSE's chief executive, outlined $20 million of additional revenues the combined group expected to earn from marrying the NYSE brand and marketing expertise to an exchange that was not subject to tough US regulatory constraints.

Euronext officials sent out different messages on Deutsche Börse. Jan-Michiel Hessels, Euronext's chairman, said: "We have a deal and we are committed."

But Jean François Théodore, its chief executive, said: "The dream of welcoming Deutsche Börse still stands. The creation of a transatlantic exchange does not change the dream of a pan-European exchange."

Mr Thain declined to speculate about "what we would do if something else happens".

However, Deutsche Börse's management made clear that it had not given up on a tie-up with Euronext. It issued a statement saying it would "continue to work toward a combination of the two companies", which, it said "would also have a significant positive impact on European financial markets".

Analysts took this as a sign that Deutsche Börse would resist a three-way tie-up. One key aspect of the deal, New York-based analysts noted, was that it contained no break-up fee, meaning that Euronext was free to walk away if a better offer was made.

Euronext directors faced questions on why they had failed to improve on terms offered two weeks earlier.

Mr Hessels said improvements had been made to the governance structure so that representatives of each of the company's markets would be guaranteed places on the board.

But Mr Théodore defended the price, which did not include a premium for loss of control, saying: "There is no premium because it is not a takeover."

NYSE's shares gained in morning trading in New York as traders began to treat a final NYSE-Euronext merger as the most likely outcome.