Nasdaq's recent bid to takeover the London Stock Exchange failed

But OMX has admitted it is in talks with several exchanges and other firms about "possible forms of cooperation".

The statement followed reports in a Swedish newspaper that US hi-tech stock market Nasdaq had made a 23bn Swedish kronor ($3.33bn; �1.7bn) bid for OMX.

The group operates stock markets in Helsinki, Stockholm, Reykjavik, Copenhagen and the Baltic countries.

It also makes trading technology for exchanges.

Shares in the exchange rose as much as 17% , before settling 11% ahead at 177 kronor.

According to a report in Sweden's Dagens Industri newspaper Nasdaq made a 192 crowns-a-share offer for the firm two weeks ago.

"Following media speculation, OMX confirms that it is in exploratory discussions with several exchanges and other market venues regarding possible forms of cooperation," OMX said.

However, spokesman for the group refused to name any of the parties it was holding talks with. Nasdaq also declined to comment on the reports.

Merger speculation

The claims came a day after the Wall Street Journal suggested Nasdaq has been in talks with the Philadelphia Stock Exchange about a possible takeover.

According to the report a takeover of the third largest options exchange in the US could be worth between $250m and $300m.

Merger speculation about various world exchanges has been rife recently as competition between exchanges has been increasing.

In the past few months, the New York Stock Exchange has taken over Paris-based bourse Euronext which controls the Paris, Brussels, Lisbon and Amsterdam exchanges, as well as the London-based Liffe international derivatives exchange.

Meanwhile, the London Stock Exchange has been the target of a number of takeover attempts.