US President Donald Trump has announced he will double the proposed tariffs on Canadian aluminum and steel imports, bringing the total to 50%.

The move comes just a day after the US stock market dropped to its lowest in years, and a week after he announced a one-month pause on the tariffs going into effect.

In a post on his Truth Social platform, Trump said he had instructed his commerce secretary to add an additional 25% tariff on steel and aluminum products from Canada that will go into effect on Wednesday. 

The post immediately caused another stock market drop.

Trump also threatened additional tariffs on imported cars if Canada does not drop its tariffs. 

The White House announced the original 25% tariffs on Canadian goods in early February, justifying the move by claiming the "threat posed by illegal aliens and drugs" was not being handled. The tariffs came into force in early March, but within days were paused after Canada agreed to send additional troops to the border.

On Monday, the premier of Ontario — a border province which supplies energy to the US states of New York, Michigan and Minnesota — announced he would be imposing a 25% cost hike on electricity for American customers. He also urged other premiers to set their own price increases on key export goods.

Trump's announcement on Tuesday comes in direct response to Ontario's move. 

He also reiterated his desire to incorporate Canada into the United States, saying "the only thing that makes sense is for Canada to become our cherished Fifty First State. This would make all Tariffs, and everything else, totally disappear."

He then called the US-Canada border an "artificial line of separation drawn many years ago," a false claim he has made before.

Edited by: Natalie Muller