South Korean mobile telecommunication operator SK Telecom Co. on Monday agreed to sell back its 3.8 percent stake in China Unicom (Hong Kong) Ltd. for KRW1.5 trillion ($1.28 billion), marking the end of a three-year investment partnership.

The announcement comes on the heels of a recent move by the Chinese telecommunication operator to deepen its ties with Spain''s Telefonica.

Telefonica and SK Telecom interestingly came forth as key associates to China Unicom after the reorganization of the domestic telecom industry this year that brought the total telecom companies from four to three.

SK Telefonica, which replaced SK Telecom as Unicom’s biggest overseas investor last year, said Monday in a statement that the sale followed a "change of strategy" and payoffs will be deployed in strengthening its financial base and tap new business opportunities.

However, both SK and Unicom said they will continue to be partners, without elaborating.

SK Telecom says it expects the transaction to close mid November after China Unicom's independent shareholders approve the plan.

Telefonica said this month it will increase its stake in Unicom to 8.1 percent from 5.4 percent.

SK Telecom bought $1 billion worth of bonds in China Unicom in 2006 and later converted the investment into shares in the Chinese carrier for HK$8.63 per share.