Mazda Motor Corp. on Wednesday posted a 17 percent drop in operating profit for the first quarter, as a rise in discounting on U.S. vehicles and costs to improve its dealership network in the country overshadowed an increase in sales.

Operating profit at Japan's fifth-largest automaker was ¥33.1 billion ($295.48 million) for the April-June period, versus ¥39.9 billion a year ago.

Mazda reiterated its forecast for a 28 percent drop in operating profit to ¥105 billion in the year ending March, the weakest since 2013, as it expects the U.S. upgrade costs and a strong yen to drag on earnings even as it extends a six-year run of rising vehicle sales.