Nasdaq is to put its 31 per cent stake in the London Stock Exchange up for sale as it steps up its fight for OMX, the Nordic exchange and technology group.

The US exchange said it would use the proceeds from any sale to buy back shares, boosting the value of its agreed cash and shares offer for OMX.

Announcing the move yesterday, Nasdaq said its own share price did not adequately reflect the value of its holding in the LSE, which it acquired at an average price of about £11 a share.

Last week, Borse Dubai made an offer to acquire OMX at SKr230 a share in cash compared with the SKr208 price that Nasdaq's own offer, agreed in May, placed on the exchange.

A sale of its LSE stake could make it easier for it to offer more to OMX shareholders.

Nasdaq said it would use proceeds from the sale to pay down debt as well as to repurchase shares.

OMX's management has said it still was recommending the Nasdaq offer. Regulators in the Nordic region are examining the circumstances under which Borse Dubai acquired a stake through options agreements with OMX shareholders.

However, the gap between the offer made by Borse Dubai and that of Nasdaq could increase pressure on OMX's management to shift its stance unless it can show that the less-generous offer is better for shareholders.

Nasdaq acquired its stake in the LSE last year. Its hostile bid for the company at £12.43 a share was rebuffed by the LSE's management, which deemed it so far below the company's actual value that it was not even worth discussing.

Nasdaq's prospects of eventually acquiring the company were further diminished by the LSE's agreed, all-share bid to buy Borsa Italiana.

In making its bid for the LSE last year, Nasdaq stressed that the fierce competition for share trading in the US was likely to become a feature of the European market once new rules, known as Mifid, took effect in November.