OMX shares surged over 18% to SKr188.50 in morning trading after the vendor released a statement confirming media speculation and saying it is in "exploratory discussions with several exchanges and other market venues regarding possible forms of cooperation".

Further details of OMX's potential suitors were not disclosed, but the exchange went on to say that "no offer, formal or informal, has been received by the company".

The statement follows a report in Swedish business newspaper Dagens Industri that OMX had received a preliminary takeover approach worth Skr23bn from Nasdaq.

The US market operator is thought to have offered 192 crowns per share in an indicative bid nearly two weeks ago, although the report says that the bid level was uncertain.

The Scandinavian firm opened its books for Nasdaq due diligence last week and the OMX board is set to meet on Thursday to discuss the bid, according to the report.

The latest speculation follows reports last September that OMX was in preliminary talks to be acquired by Nasdaq. OMX was thought to be looking to cash in on the wave of exchange consolidation sweeping the European and US markets.

The Nordic and Baltic market operator has previously been the subject of bid talk from a number of potential buyers, including the LSE. OMX also tried to buy the UK exchange and originally launched a hostile takeover in 2000, but this was rejected by the LSE.

Nasdaq has not made any comment on the latest speculation, which comes amid reports earlier this week that it was looking to takeover the Philadelphia Stock Exchange (PHLX) in a bid to expand in options trading.

Discussions between Nasdaq and PHLX are thought to have intensified in the last few weeks as Nasdaq looks for its next step after failing in its bid to buy the London Stock Exchange.