OTTAWA — Canada's retaliatory tariffs on U.S. goods took effect after midnight on Tuesday, intensifying an 18-month-old trade war and spurring Prime Minister Mark Carney to urge a further shift away from the country's biggest trading partner. The Canadian levies follow 50 percent tariffs the United States imposed on some $20 billion of Canadian goods last month, after several rounds of negotiations collapsed. The breakdown has widened a rift between the longtime allies, both of whom have blamed the other for the failed talks. "We have everything we need to pivot and prosper," Carney said on Tuesday in a video posted on YouTube after the tariffs came into effect. "That pivot will come at a cost. There's always a cost to action. But it doesn't come close to the cost of standing still," he said. A government source said there are currently no talks between the two sides on the level of ministers or government officials. Ottawa designed the retaliatory measures to put economic and political pressure on Washington, Canadian government officials said, and the tariffs are expected to hit secto