Turkey's currency slumped to a new record low as Donald Trump compounded the country's economic crisis by doubling steel and aluminium tariffs.
The US president revealed the action on Friday as he noted how the Turkish lira "slides rapidly downward" against the "very strong" US dollar.
Amid an escalating feud with Ankara, Mr Trump added on Twitter: "Our relations with Turkey are not good at this time!"
The day saw the lira plunge as much as 18% at one point, the biggest one-day drop since Turkey's 2001 financial crisis.
Now at a new record low, Turkey's currency has lost more than 40% this year.
The slump is attributed to the tensions with the US and concerns about President Recep Tayyip Erdogan's control of monetary policy.
There are now fears the weakening lira will see Turkish companies that borrowed heavily in the country's construction boom struggle to repay loans in dollars and euros.
The White House cited national security grounds as the means by which Mr Trump had authorised a 50% steel tariff and 20% aluminium tariff on Turkey.
This is double the level the president imposed on a range of countries earlier this year, including EU member states.
But Turkey's trade ministry said the tariffs were against World Trade Organisation rules.
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!
— Donald J. Trump (@realDonaldTrump) August 10, 2018
Mr Erdogan also remained defiant, as he urged the Turkish people to exchange foreign currency or gold for lira.
"If there is anyone who has dollars or gold under their pillows, they should go exchange it for liras at our banks," he said during an address to supporters.
"This is a national, domestic battle."
He railed against "those waging economic war" against Turkey.
But the trade minister, Ruhsar Pekcan, said: "We implore President Trump to return to the negotiating table."
Mr Trump has castigated Turkey for detaining American pastor Andrew Brunson, who is on trial for terrorism charges for allegedly associating with plotters of the failed 2016 coup against Mr Erdogan.
Observers have noted how fighting for Mr Brunson's cause is likely to be popular with Mr Trump's evangelical base ahead of crucial mid-term elections this November.
Meanwhile, Ankara is wanting the extradition of Fethullah Gulen, a Pennsylvania-based cleric who is blamed by Mr Erdogan for masterminding the 2016 coup.
The Turkish president took aim at the US in his address, claiming "some countries have engaged in behaviour that protects coup plotters and knows no laws or justice".
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He added: "Relations with countries who behave like this have reached a point beyond salvaging."
On Friday, Mr Erdogan also held a telephone call with Russian President Vladimir Putin, with the pair discussing economic ties between their two countries.