Nasdaq has increased its stake in the London Stock Exchange to 18.7% after buying a further 9.79 million shares for £119.2 million. The news comes as pan-European exchange Euronext says it is no longer holding merger talks with the UK market operator.
Nasdaq said last month that it had became the UK exchange's largest shareholder after acquiring a 14.99% stake in the business.
The US exchange operator bought the stake less than two weeks after dropping its £2.43bn cash bid for the LSE. However, under UK takeover laws, Nasdaq must wait six months from that date before making another bid unless the LSE backs a revised offer or receives a bid from a third party.
LSE shares were up 3.10%, or 37.50 pence to 1225.00 pence in afternoon trading after Nasdaq said it has increased its stake in the business.
News of Nasdaq's purchase follows an announcement by Euronext that it had ended merger talks with the LSE but was still in active discussions with Deutsche Börse.
In a statement ahead of its AGM next month, Euronext says: "In light of the acquisition of a 15% stake in London Stock Exchange plc by The Nasdaq Stock Market, Inc., Euronext confirms that it is no longer in discussions with LSE regarding a possible offer for the company."
Euronext says shareholders at its AGM will vote on a resolution proposed by an investor that a merger with Deutsche Börse is in the best interests of all its shareholders.
But Euronext's board is advising shareholders to vote against the resolution, saying that the company "is concerned not to restrict its flexibility during this period".