Samsung Electronics Co Ltd, the world's No.2 handset manufacturer, plans to roll out a new version of its flagship smartphone Galaxy S in South Korea this month through KT Corp, the telecommunications operator said on Friday.

The local debut of the ultra-slim Galaxy S II comes after bigger rival Apple Inc introduced the iPhone 4 in South Korea in September, expanding the offering by ending an exclusive deal with KT and adding SK Telecom Co Ltd last month.

South Korea is one of the most lucrative markets for Samsung's smartphones. It sold about 2 million Galaxy S handsets last year, one-fifth of the total global shipments.

KT, South Korea's second-biggest mobile carrier, said on Friday that it planned to release the new model around April 25. Bigger rival SK Telecom said it had yet to decide a launch date.

Samsung declined to reveal launch details but said the smartphone, based on Google Inc's Android operating system, would be rolled out in April as planned.

(Reporting by Hyunjoo Jin and Miyoung Kim; Editing by Chris Lewis)