Samsung Electronics Co Ltd. on Thursday reported its worst quarterly profit in two years and was downbeat about its second-half prospects, fuelling concerns about its ability to protect its smartphone turf in the face of mounting competition. With its flagship Galaxy S5 smartphone outsold by Apple Incs iPhone 5S in May and its cheaper devices feeling the squeeze from Chinese rivals like Xiaomi, Samsung is under pressure to come up with a new strategy to halt the slide. For April-June, Samsung said operating profit fell 24.6 percent annually to 7.2 trillion won ($7.03 billion), matching its guidance. Profit for the mobile division fell to 4.42 trillion won from 6.28 trillion won a year ago, also the lowest in two years.