OTTAWA (Reuters) - Canada is imposing 25% tariffs on C$30 billion worth of U.S. imports effective immediately, Prime Minister Justin Trudeau told reporters on Tuesday.

Trudeau made the announcement just hours after U.S. President Donald Trump slapped 25% tariffs on imports from Mexico and Canada.

"There is absolutely no justification or need whatsoever for these tariffs today," Trudeau said, adding that Canada would challenge the U.S. measures at the World Trade Organization and through the U.S.-Mexico-Canada trade agreement.

If the U.S. tariffs persist, Canada will impose a 25% tariff on a further C$125 billion of U.S. imports in 21 days' time, he said.