Donald Trump has hit back at Canada after a breakdown in negotiations plunged the two countries into a trade war.

In his first public comments since negotiations collapsed on Friday in Washington, the US president wrote on social media: “Canada wants the benefits of being a State, without being one!!!”

“They have also charged our great farmers, for many years, massive amounts of tariffs,” he added. “No more!!!”

His comments came after the US imposed 50% tariffs on $20bn (£14.6bn) worth of Canadian goods, while Mark Carney, the country’s prime minister, has vowed to match them “dollar for dollar”.

The US tariffs came into force on Saturday, ranging from hockey sticks to tongue depressors. Trade experts have predicted that the tariffs could result in some job losses, but the biggest impact is expected to be political, triggering fresh tension between the neighbours.

Both sides blamed the other for the breakdown in talks on Friday. Carney told Canadian journalists that the country was “at war” over trade with the US, after Trump “miscalculated” by escalating his tariff attack.

“You’re at war when you’re attacked, and we got attacked,” the Canadian prime minister told reporters in Ottawa. “We cannot accept what they’ve offered and we will not give what they’ve asked.”

Jamieson Greer, the US trade representative, has said the US was compelled to act after a year of retaliatory measures by Canada. He told Fox & Friends Weekend: “We’ve said enough and so we’ve taken countermeasures. Our interest is in protecting American workers and protecting American supply chains.”

Carney, who previously served as the governor of the Bank of England, was elected as Canada’s prime minister last year after campaigning to lead a fightback against Trump, who has previously suggested he wants to make Canada a 51st state with “economic force”.

Carney’s “dollar for dollar” tariffs are expected to take effect from 8 September, with new levies on steel, dairy, appliances and electronics. The escalation has also called into question the future of the North American trade pact between the US, Canada and Mexico, known as USMCA.

The pact, which was signed by Trump during his first term, governs about $2tn annually in goods and services between the three countries. Trump refused to renew the USMCA this summer after Canada and Mexico formally requested for it to be renewed for another 16 years.

When asked how the US-Canadian collapse in trade talks would affect the USMCA, Carney said it was “certainly not good news”.