WASHINGTON — President Donald Trump said Friday he would double the rate of tariffs on steel and aluminum imports from Turkey, inflicting additional pain on President Recep Tayyip Erdogan, whose country is in an economic crisis.

Trump’s abrupt and unilateral action came amid worsening relations with Turkey, which has continued to detain an American pastor on espionage charges despite the U.S. insistence that he be released.

In a Twitter post Friday morning, Trump said the U.S. would bump Turkey’s aluminum tariffs to 20 percent and steel tariffs to 50 percent and cited the country’s deteriorating currency, the Turkish lira.

While Trump’s decision is primarily aimed at punishing Turkey over its failure to return the pastor, Andrew Brunson, the decision spooked markets and raised the possibility that he could similarly raise tariff rates on other trading partners that have seen their currencies fall against the strengthening dollar, most notably China. Trump has already threatened to increase tariff rates on $200 billion worth of Chinese goods to 25 percent from 10 percent, in part because of the sharp decline in its currency.

The S&P 500 fell 0.7 percent. The dollar, as measured by the ICE U.S. dollar index, was up more than 0.8 percent. Investors flocked to the safety of U.S. government bonds, pushing yields lower. The yield on the 10-year Treasury note fell to 2.87 percent, a sign that investors were hungry for security.

Trump’s mention of the currency suggested he is concerned a rapid depreciation in Turkey’s currency has essentially mitigated the effect of his tariffs. Since a weaker currency makes it less expensive for countries to export, the tariffs carry less punch. By doubling the rate, Trump’s levies will continue to hurt exporters.

Ruhsar Pekcan, the Turkish minister of trade, said Turkey was “deeply disappointed” by the decision. “The tariffs were groundless when they were announced in June, and remain so now,” Pekcan said.

A White House spokeswoman, Lindsay Walters, said Friday that the president had authorized the increase based on a threat to national security.