Entrepreneur Denis O'Brien looks set to further build up his stake in Independent News and Media (IN&M), according to market sources.

Representatives of Mr O'Brien were looking to acquire more shares in IN&M last week, but it is not clear whether the transactions were completed. Some shares held by a major institution, most likely the US mutual fund Fidelity, are believed to have come on the market. Mr O'Brien's long-term intentions in relation to IN&M are unclear.

The number of shares Mr O'Brien is seeking to acquire has not been disclosed and he declined to comment through his spokesman yesterday. Almost 13 million IN&M shares were traded last Friday in Dublin. Some market sources said Mr O'Brien traded in shares and an announcement could be made in coming days.

It is understood some shares at €2.60 became available but were not purchased. A smaller number at a cheaper price may have been acquired. The IN&M share price closed on Friday evening at €2.55. The shares performed well during the week on the back of healthy 2005 results.

Mr O'Brien spent nearly $56.5 million in January buying a 3 per cent stake in IN&M, the company run and partly-owned by his long-standing business rival, Sir Anthony O'Reilly.

Mr O'Brien acquired 22.6 million shares in the publishing group, which he once accused of making "outrageous attacks" on him.

In January a spokesman for the company welcomed Mr OBrien's investment. "Independent is one of the best growth prospects of any media organisation," the spokesman said.

Mr O'Brien, who became one of the richest men in the State when he netted €290 million from the sale of his Esat business to British Telecom, has locked horns with Sir Anthony over several high-profile business deals in recent years.

Most notably, Sir Anthony led the Valentia consortium which outbid Mr O'Brien's eIsland group to buy Eircom and subsequently take it private in 2001.