Officials have issued an air-quality health alert after smoke blanketed New York and New Jersey

US President Donald Trump has threatened to impose additional tariffs on Canada over wildfire smoke that has blanketed much of the northeastern United States, just days before the FIFA World Cup final in New Jersey.

Trump accused Ottawa on Friday of failing to manage its forests and allowing what he described as "filthy, polluted, and unhealthy air" to cross the border.

"We are holding Canada responsible for the fact that they are not properly maintaining their Forests, and Brush therein," Trump wrote on Truth Social, claiming that the pollution was costing the US "billions of dollars."

"This is Willful Negligence, and becoming a yearly occurrence," he added, arguing that the alleged cost "must of necessity be added to the TARIFFS Canada is currently paying." Trump said he planned to call Canadian Prime Minister Mark Carney to ask what Ottawa intended to do about the fires.

Ontario Premier Doug Ford earlier rejected criticism from US politicians, pointing to Canadian assistance during American wildfires and hurricanes. "Maybe what you should do rather than complain is send support, send help," he said.

Canada's wildfire activity intensified in late June amid hot, dry conditions, with several major blazes in northwestern Ontario expanding sharply this week. Smoke from nearly 900 active fires reached New York City on Wednesday, pushing the Air Quality Index above 200 in some areas by Thursday evening - a level classified as "very unhealthy."

Air-quality alerts remained in effect across New York City, Long Island and parts of northern New Jersey through Saturday, including Bergen County, where MetLife Stadium is located. Officials warned that fine-particle pollution could reach unhealthy levels and urged residents - particularly children and people with heart or respiratory conditions - to limit outdoor exertion, stay indoors where possible and wear an N95 or KN95 mask outside.

The air-quality hazard comes days before Argentina and Spain are due to contest the final at the open-air MetLife Stadium in East Rutherford, New Jersey. Around 80,000 spectators are expected to attend Sunday's 3pm kickoff.

Authorities and FIFA officials are monitoring conditions, although sources told ESPN that the final is not currently considered to be under threat. Rain and changing winds could improve air quality before kickoff, but forecasters cautioned that another mass of smoke could move into the region after the rain passes.