The World Trade Organization (WTO) has upheld a ruling that supported steep anti-dumping tariffs imposed by the United States on imports of Canadian softwood lumber, but maintained that U.S. authorities miscalculated the amounts, according to the Associated Press.

Canada and the United States had both appealed the earlier decision by a WTO panel, but a 63-page final ruling rejected challenges by both countries.

A panel of three trade experts rejected claims by the Canadian government that the United States had acted illegally in investigating whether lumber from Canada was being sold at prices below the cost of production-a practice known as dumping.

Rejecting the U.S. appeal, the panel also upheld an earlier ruling that the U.S. government's calculations were wrong because Washington used a method called "zeroing," in which sales at above-market prices are ignored.

The panel said the WTO should order the U.S. government to change its calculation methods to conform with WTO rules. The U.S. will have to recalculate the level of the duties. It was unclear what the new figure would be.