Donald Trump has announced plans to raise tariffs on Canadian goods in response to wildfire smoke drifting across the border, which he said was causing "incalculable" damage to the US.
Around 100 million Americans are currently experiencing air quality rated as "unhealthy", "very unhealthy" or "hazardous" as smoke from Canadian wildfires spreads across the Midwest, Mid-Atlantic and Northeast.
The US President took to Truth Social to condemn Canada's handling of the crisis, declaring: "The United States is being unnecessarily invaded by filthy, polluted, and unhealthy air, the quality of which is dangerous, and totally unacceptable!"
Smoke has blanketed several major cities along the eastern seaboard, including New York, Washington DC, Boston, Philadelphia and Baltimore, leaving the skyline shrouded in thick haze.
The Statue of Liberty was barely visible through the smog for three consecutive days between July 15 and 17.
Health experts have warned that the poor air quality is worsening symptoms among people with respiratory and cardiovascular conditions.
Those with asthma and heart disease are considered among the most vulnerable to the elevated pollution levels.
Mr Trump accused Canada of failing to properly manage its forests, branding the situation an act of deliberate carelessness that had become an annual problem hitting American taxpayers hard.
Mr Trump accused Canada of failing to properly manage its forests
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"Canada has refused to engage in basic Forest Management and Debris Removal, knowing that such refusal will lead to exactly this result," he wrote.
"This is Willful Negligence, and becoming a yearly occurrence, costing the United States Billions of Dollars, which cost of this pollution must of necessity be added to the TARIFFS Canada is currently paying."
The President said he would call the Canadian Prime Minister to demand answers over how Ottawa intended to tackle the crisis.
Canadian authorities said 858 wildfires were currently burning across the country, with six communities in Ontario placed under evacuation orders.
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Smoke has blanketed several major cities along the eastern seaboard, including New York
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The announcement comes amid already strained relations between Washington and Ottawa, with the two countries locked in a row over Mr Trump's delay in opening the Gordie Howe International Bridge linking Windsor, Ontario, with Detroit, Michigan.
The President has also repeatedly suggested Canada should become America's "51st state".
Most Canadian goods are currently subject to a 10 per cent global import tariff, which is due to expire on July 24.
Steel, aluminium and copper face duties of between 15 and 20 per cent, while Canadian vehicles are subject to tariffs of 25 per cent.
Canadian authorities said 858 wildfires were currently burning across the country
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Fears are also growing that the poor air quality could disrupt Sunday's World Cup final in New Jersey.
Fifa said on Friday that it was “monitoring the situation closely”, but added that it did not expect the clash between Argentina and Spain to be affected.
Andrew Giuliani, who heads the White House Fifa task force, told reporters: “There’s been discussion about it, and we have somebody with the National Weather Service that sits in FIFA headquarters."
A White House spokesman told The Telegraph: “President Trump has numerous tariff powers at his disposal, and he is committed to leveraging every lever of executive power to ensure the health and safety of the American people.”