Oslo Bourse is inviting rival bidders to a EUR625 million takeover offer tendered by Euronext on Christmas Eve last year.
Euronext claimed last month to have secured the backing of a majority of Oslo Bors shareholders for its tender offer in January, but Oslo Bourse believes the timing of the bid put potential alternative buyers at a disadvantage.
In a statement, the exchange operator says: "The Board of Oslo Børs VPS Holding has decided to invite relevant parties that may be interested in the opportunity of making an offer for shares in Oslo Børs VPS to participate in an offer process."
The extended auction period will take place later this month, with the aim of ensuring that Euronext's offer is in "best interests of shareholder value and the Bourse's stock exchange and central securities depository activities".
The Board says it intends to hold meetings with Euronext and other interested parties before it issues its evaluation and recommendation to shareholders.