Samsung staked its claim to the high end of the smartphone market Thursday, unveiling two large-screen handsets and its new mobile payment system as part of its challenge to Apple. The moves are aimed at keeping the South Korean giant atop the global smartphone market and countering its U.S. rival Apple, which has made gains with its large-screen iPhone 6 and 6-Plus and its tap-to-pay feature. At a New York media event, Samsung unveiled its Galaxy S6 edge+, the latest update for its flagship handset, and Galaxy Note5, its main device in the "phablet" market."Today the journey continues in the large-screen category that Samsung created," said J.K. Shin, Samsung's head of IT and mobile communications. The S6 edge+ and Note5 each have a 5.7-inch display, but the S6 has smaller overall dimensions and a curved "dual edge" screen that sets aside a portion of the display for contacts or other content.The company also announced that its Samsung Pay service would roll out in South Korea on Aug. 20 and in the U.S. on Sept. 28, and that it would launch in Britain, Spain and China with partners to be named in each market. Shin said he expects wide adoption because Samsung Pay "doesn't cause small business to upgrade their terminals and will be accepted almost everywhere on day one."Samsung said its mobile service can be used with magnetic stripe terminals as well as those using updated NFC or "near field communication" contactless payments employed by Apple Pay. InJong Rhee, Samsung Electronics vice president, said: "NFC is fine technology but most stores don't have it."He added that Samsung Pay will be secured by its Knox software, which creates a one-time code without transmitting credit card numbers. Samsung has remained atop the global smartphone market even though its sales have been slipping in the past year.With the new devices, Samsung expands from its 5.1 inch display on the existing Galaxy S6, and leapfrogs Apple's handsets at 4.7 and 5.5 inches.