Tensions have been high between two NATO allies over detention of evangelical pastor. (Reuters)

U.S. President Donald Trump said on Friday he had authorized higher tariffs on imports from Turkey, imposing a 20 percent duty on aluminum and 50 percent one on steel, as tensions mount between the two NATO allies over Ankara's detention of an evangelical pastor and other diplomatic issues.

"I have just authorized a doubling of Tariffs on Steel and Aluminum with respect to Turkey as their currency, the Turkish Lira, slides rapidly downward against our very strong Dollar!" Trump said in an early morning post on Twitter.

"Aluminum will now be 20 percent and Steel 50 percent. Our relations with Turkey are not good at this time!"

Trump's announcement came less than an hour after Turkish President Tayyip Erdogan urged Turks to help defend the country against what he called economic war against the country. Erdogan appealed to a crowd in the city of Bayburt to exchange dollars and gold for Turkish lira to prop up the plunging currency.

The United States, the world's biggest steel importer, imposed tariffs of 25 percent on steel and 10 percent on aluminum in March for imports from a variety of countries.

Since then, its relationship with Turkey, the sixth largest steel importer to the United States, has deteriorated, prompting Ankara to send a delegation this week to Washington to meet with both the State and Treasury Departments. But those talks on Thursday showed no signs of breakthrough.

Last week, the United States imposed sanctions on Turkey's justice minister and interior minister for not releasing pastor Andrew Brunson.

Securing the release of Brunson, arrested in 2016, is a top priority for the United States, and it is also tussling with Turkey over the detention of three locally employed U.S. embassy staff, trade issues and differences over Syria.

© Thomson Reuters 2018