President Donald Trump said Friday he has green-lit a doubling of steel and aluminum tariffs on Turkey and warned that relations between the US and Turkey "are not good at this time," a move that comes amid US efforts to increase pressure on Ankara to secure the release of an American pastor.

"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! Aluminum will now be 20% and Steel 50%. Our relations with Turkey are not good at this time!," the President tweeted.

Friday's announcement could further escalate tensions with Turkey, which continues to detain Andrew Brunson, an American pastor Ankara accuses of helping plot a 2016 coup attempt against Turkish President Recep Tayyip Erdogan. Earlier this month, the US slapped sanctions against Turkey's ministers of justice and interior in response to Brunson's detention.

Trump and Erdogan have discussed Brunson's imprisonment "on several occasions," White House spokesman Sarah Sanders said at the time, adding that Trump is "not happy with Turkey's decision not to release" the pastor.

Since then, the situation appears to be escalating. On Saturday, Turkey ordered that the assets of the US "justice and interior" secretaries would be frozen.

A Turkish delegation was in Washington this week to discuss the Brunson situation, meeting with officials at the State Department and other agencies, but those talks appear to hit a dead end.

"Yesterday we had a wide-ranging conversation with Turkish Government officials," State Department spokesman Heather Nauert said Thursday. "We made it clear that Pastor Brunson needs to be returned home ... The progress that we want to be made is to have Pastor Brunson return home. And I'll leave it at that."