MADRID, Feb 2 (Reuters) - Spain's Telefonica SA and fashion retailer Zara's owner Amancio Ortega agreed to buy the 40% stake in mobile phone mast operator Telxius that belong to KKR for 216 million euros ($243.45 million), Telefonica said late on Tuesday.

Telefonica and Ortega, through his family office Pontegadea, will become the sole shareholders in Telxius through their joint-venture called Pontel, Telefonica said in a filing to the market regulator.

Simultaneously, Pontegadea will raise its stake in Pontel to 30% from 9.99%, the filing said.

($1 = 0.8872 euros) (Reporting by Corina Pons, editing by Inti Landauro)