Apple CEO Tim Cook espoused the virtues of free trade and bashed tariffs at an economic forum in China on Saturday, amid growing fears of a potential trade war between the U.S. and China.

The Wall Street Journal reports that Cook spoke at the China Development Forum in Beijing where he warned that countries that pass tariffs and engage in protectionist trade policies don't perform "exceptionally" in the global market.

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“Countries that embrace openness, that embrace trade, that embrace diversity are the countries that do exceptionally,” Cook said when asked what message he would like to send to Trump. “And the countries that don’t, don’t.”

Cook did not directly criticize new metal tariffs put in place by President Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE last week. Trump went ahead with his plan to impose a 25 percent tariff on imported steel and 10 percent tariff on imported aluminum despite opposition from his own party.

The iPhone, Apple's most popular product, is designed in California but assembled overseas in China.

Trump announced billions of dollars in additional tariffs on Chinese products this week, characterizing it as part of a push to curb efforts to steal U.S. intellectual property from American companies.

Beijing responded with a reciprocal plan to levy tariffs of 25 percent on pork imports from the U.S. and 15 percent tariffs on U.S. steel pipes, fruit, and wine.

Chinese officials have called on the Trump administration to resolve the trade issues through diplomatic talks.

But Trump on Friday alluded to more potential trade action against Beijing over stolen intellectual property, adding that action against China is "going to make us a much stronger, much richer nation.”

“We want reciprocal, mirror,” he said. “If they charge us, we charge them the same thing. That’s the way it’s gotta be.”