US President Donald Trump Mr Trump announced on Twitter last week that he had authorised a doubling of duties on aluminium and steel imported from Turkey, putting unprecedented economic pressure on Ankara.
U.S. Treasury chief Steve Mnuchin earlier said the U.S. could put more sanctions on Turkey. Turkey and Qatar - which is also a very close USA ally - have become close economic and political partners in recent times.
He also urged Brunson to serve as a "great patriot hostage" while he is jailed and criticized Turkey for "holding our wonderful Christian Pastor".
Last week, the USA doubled its tariffs on metal imports from Turkey. "He's a very innocent man", President Trump remarked at a Cabinet meeting Thursday.
Following the announcement, the lira firmed briefly to 5.8699 from 6.04 to the US dollar, but later eased back to 6.0200 at 1538 GMT.
The lira has clawed back some ground over the past two days - after losing nearly a quarter of its value on Friday and Monday - but economists are warning that Turkey must urgently address its economic imbalances to avoid more trouble.
Investor attention was focused on a conference call which Finance Minister Berat Albayrak will hold at 1300 GMT to reassure global investors.
Turkey has been hit by a currency crisis fuelled by a heated row with the United States. "Our relations with Turkey are not good at this time!"
Qatar poured funds into the country the same day Turkey doubled tariffs on some USA imports, such as cars, alcohol and tobacco, one day after President Recep Tayyip Erdogan called for a boycott of iPhones. Investors also fret over Erdogan's influence over monetary policy.
In an article for the New York Times, published last Friday, the Turkish leader said Turkey "had rushed to America's help whenever necessary" in various times, from the Cold War to the more recent conflicts in Afghanistan, Iraq and Syria.