Canada’s retaliatory tariffs on $28-billion worth of U.S. imports took effect early Tuesday, as Prime Minister Mark Carney fired back at President Donald Trump’s trade war and braced for an expected counterpunch from Washington.

Mr. Carney’s office said Monday that there had been no eleventh-hour talks to prevent Canada from imposing imposing the countertariffs.

Instead of negotiations over the weekend, Mr. Trump made a steady stream of derisive and insulting social media posts about Canada and floated a ban on Canadian luxury-jet maker Bombardier.

The attack on the prominent Canadian company was made only on social media, with no formal policy announcement from the White House.

Ottawa’s levies on American businesses came into force at 12:01 a.m. Tuesday. They include nearly 900 items – everything from clothing and home appliances to metals and electronics.