By Nick Kostov 

PARIS -- French media company Vivendi SA said Monday it was ready to buy up to 30% in Mediaset SpA, a move that is likely to escalate tensions with the Italian broadcaster's founder, former Prime Minister Silvio Berlusconi.

Vivendi, led by billionaire Vincent Bolloré, said last week it held 20% of Mediaset. A 30% stake is the legal threshold before an investor is required to launch a takeover offer for all shares outstanding.

"Vivendi's Management Board met today and decided, with the Supervisory Board's authorization, to increase its investment in Mediaset by acquiring additional shares depending on market conditions within the limits of 30% of the share capital and voting rights," the French company said in a statmement.

Vivendi said its decision to buy more shares followed a meeting between its Chief Executive Arnaud de Puyfontaine and his counterpart at Mediaset, Pier Silvio Berlusconi, and took into account the "recent positions" of Italy's Fininvest, Mediaset's biggest shareholder. It didn't elaborate.

A representative for Mediaset said Monday that he had no further comment.

Fininvest, the holding company controlled by the Berlusconi family, holds 39.8% of Mediaset's voting rights. The firm has called Vivendi's move "hostile" and lodged a complaint in Milan last week against the French company for market manipulation.

The planned stock purchase raises the stakes in the battle between two of the world's biggest media moguls. Mr. Bolloré, who as chairman of Vivendi calls the shots with a stake of over 20%, has made a fortune over the past three decades seizing control of businesses, which has earned him a reputation as a skilled, if unpredictable, corporate tactician.

In training his sights on Mr. Berlusconi, Mr. Bolloré is taking on a wily businessman and politician, who has outsmarted his adversaries for decades, in part by using his political influence to move the regulatory goal posts and protect his business interests.

In the statement, Vivendi said it "its presence in the Mediaset equity is in line with the group's intention to develop its activities in southern Europe and its strategic ambitions as a major international, European-based, media and content group".

Manuela Mesco contributed to this article.

Write to Nick Kostov at Nick.Kostov@wsj.com

(END) Dow Jones Newswires

December 19, 2016 14:38 ET (19:38 GMT)