U.S. President Donald Trump threatened Friday to raise tariffs on Canada, arguing the additional duties should offset the economic costs of wildfire smoke that has blanketed large swaths of the United States.

Dense smoke drifting south from wildfires in Canada and northern Minnesota has triggered unhealthy air quality alerts across large parts of the United States.

As of Saturday, Canada had 937 active wildfires, most of them burning out of control, according to the Canadian Wildland Fire Information System.

"This is Willful Negligence, and becoming a yearly occurrence, costing the United States Billions of Dollars," Trump wrote on Truth Social, adding that "the cost of this pollution must of necessity be added to the TARIFFS Canada is currently paying."

Trump also accused Canada of failing to properly manage its forests, saying it had neglected "basic Forest Management and Debris Removal."