Samsung Electronics Co Ltd flagged a 10 percent jump in quarterly profit on Thursday - a sign of robust early sales for its new Galaxy S7 smartphones although doubts abound whether momentum can be maintained in the face of new rival offerings. The South Korean tech giant's estimate for first-quarter operating profit handily beat market forecasts and has boosted hopes that its struggling mobile business will post its first annual profit gain in three years, also benefiting from an improved performance for mid-to-low tier devices and cost-cutting efforts.