Daimler Truck's first-quarter operating profit more than halved owing to historically weak demand and import tariffs in a North American market where volumes fell to a 16-year low, the company said on Wednesday. Adjusted operating profit fell to 498 million euros ($584 million) from 1.08 billion euros a year earlier, reflecting a sharp slowdown in North America, the group's largest and most profitable market. The quarter for the first time showed full tariff effects at the group's Trucks North America division, CFO Eva Scherer said. The sales decline, import tariffs and adverse currency effects cost the North American arm 624 million euros in the quarter, the group said. Scherer added that the tariff impact alone amounted to at least 100 million euros in the first quarter. Adjusted return on sales in North America fell to 5.4% from 14.4% in the same period last year.