MADRID (Reuters) - Spain's competition watchdog CNMC said on Thursday it had opened an in-depth antitrust investigation into telecom giant Telefonica's (>> Telefonica SA) acquisition of media group Prisa's (>> Promotora de Informaciones S.A.) pay-TV firm Distribuidora de Television (DTS).

In May Prisa agreed to sell 56 percent of DTS, known as Canal+ in Spain, to Telefonica, in a deal that would now give it full control over the TV group.

"The Telefonica/DTS deal could significantly hinder competition in the markets related to paid television, audiovisual content and electronic communications services," the CNMC said in a statement.

(Reporting by Tracy Rucinski, Editing by Sarah White)

Stocks treated in this article : Promotora de Informaciones S.A., Telefonica SA