French media group Vivendi says it is acquiring up to 30 percent of Silvio Berlusconi's Mediaset empire in what the Italian company fears is aa hostile takeover attempt.

Vivendi, whose holdings include Universal Music and Canal+ pay-TV operator, said its board agreed Monday to boost its share of the Mediaset television and publishing empire through share purchases.

Tensions have mounted and trading has been volatile in Mediaset since Vivendi boosted its holdings to 20 percent last week.

Italy's government has warned Vivendi to obey the rules of the market.

Mediaset took Vivendi to court to try to recover losses after Vivendi pulled out of a bid for Mediaset's Premium unit.