(Adds source on price guidance for Mediaset shares)
MILAN, Feb 12 (Reuters) - Fininvest, the holding of former prime minister Silvio Berlusconi's family, has started placing a 7.8 percent stake in private broadcaster Mediaset to boost its own financial strength and fund a diversification of assets, it said on Thursday.
The placement will take place through an accelerated bookbuilding to Italian and foreign institutional investors starting immediately, it said without giving financial details.
Investors interested in buying Mediaset shares are being guided towards a price of 4.06 to 4.262 euros a share, a market source said. This compares with a closing price of 4.262 euros.
Merrill Lynch International and UniCredit are acting as joint bookrunners and joint lead managers.
In a statement, Fininvest said its stake in Mediaset after the placement will be 33.4 percent.
"The proceeds of the offering will be used by Fininvest, among other things, to continue to strengthen its financial and capital structure and help possible investments with a view to diversify its equity portfolio," it said.
Reporting by Silvia Aloisi and Gianluca Semeraro; editing by Paola Arosio and Elaine Hardcastle