Euronext raised its offer to 158 kroner per share, beating an offer made by Nasdaq on January 30 of 152 kroner per share, as well as its original December bid of 145 kroner per share.

That brought the total of Euronext's bid to $783 million (691 million euros) compared to Nasdaq's $770 million.

However the management of the Oslo stock exchange said it would continue to endorse Nasdaq's offer, which is has described as better for its capital market and companies.

"Our recommendation and that of the board of directors regarding the best strategic ownership remains unchanged," Bente Landsnes, the head of the Oslo Bors, told AFP.

The US-based Nasdaq controls all of the other stock exchanges in the Nordic and Baltic region, while Euronext operates the Paris, Amsterdam, Brussels, Dublin and Lisbon markets.

In addition to putting more money on the table, Euronext said its offer would help develop the Oslo stock exchange while maintaining its local identity.

"Euronext is committed to maintaining, investing in and developing Oslo Bors VPS as a key market infrastructure in Norway and internationally for the benefit of all stakeholders," adding that "continuity, local governance and decentralised decision-making are the key principles of Euronext's model."

Euronext's original offer had already attracted the binding acceptance of more than half of shareholders.

Unless either Euronext or Nasdaq withdraws its bid, the future ownership of the Oslo exchange will likely be decided by Norwegian authorities, whose approval is required for any acquisition of more than 10 percent.