ANKARA, Turkey -- Turkey and the United States exchanged new threats of sanctions Friday, keeping alive a diplomatic and financial crisis that is threatening the economic stability of the NATO country as a Turkish court rejected the appeal of an American pastor caught in the middle of the row. Turkey's lira fell once again after the trade minister, Ruhsar Pekcan, said Friday that her government would respond to any new trade duties, which U.S. President Trump threatened in an overnight tweet.

Mr. Trump is taking issue with the continued detention in Turkey of Andrew Brunson, an American evangelical pastor who faces 35 years in prison on charges of espionage and terrorism. Before leaving the White House on Friday, Mr. Trump warned that "we are not going to take it sitting down." He also called the spying charge against Brunson "phony" and denounced Turkey as a "problem for a long time."

He said Turkey has "not acted like a friend" and demanded Brunson's release, saying "they can't take our people."

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Turkey's state-run Anadolu news agency said Friday a high court in Izmir had upheld a lower court's decision earlier this week to keep Brunson under house arrest. It also rejected an appeal for his travel ban to be lifted, Anadolu reported.

Brunson's lawyer Ismail Cem Halavurt told CBS News on Friday that they may file another appeal with the court as, "depending on the developments, we can apply again." He said he was also considering an appeal to Turkey's constitutional court. Brunson's next hearing is scheduled for October 12.

Mr. Trump wrote in a tweet late Thursday: "We will pay nothing for the release of an innocent man, but we are cutting back on Turkey!"

Turkey has taken advantage of the United States for many years. They are now holding our wonderful Christian Pastor, who I must now ask to represent our Country as a great patriot hostage. We will pay nothing for the release of an innocent man, but we are cutting back on Turkey! — Donald J. Trump (@realDonaldTrump) August 16, 2018

He also urged Brunson to serve as a "great patriot hostage" while he is jailed and criticized Turkey for "holding our wonderful Christian Pastor."

U.S. Treasury chief Steve Mnuchin earlier said the U.S. could put more sanctions on Turkey.

The United States has already imposed sanctions on two Turkish government ministers and doubled tariffs on Turkish steel and aluminum imports. Turkey retaliated with some $533 million of tariffs on some U.S. imports - including cars, tobacco and alcoholic drinks - and said it would boycott U.S. electronic goods.

"We have responded to (U.S. sanctions) in accordance to World Trade Organization rules and will continue to do so," Pekcan told reporters on Friday.

Turkey's currency, which had recovered from record losses against the dollar earlier in the week, was down about 6 percent against the dollar on Friday, at 6.17.

Turkey's finance chief tried to reassure thousands of international investors on a conference call Thursday, in which he pledged to fix the economic troubles. He ruled out any move to limit money flows - which is a possibility that worries investors - or any assistance from the International Monetary Fund.

Investors are concerned that Turkey has amassed high levels of foreign debt to fuel growth in recent years. And as the currency drops, that debt becomes so much more expensive to repay, leading to potential bankruptcies.

Also worrying investors has been President Recep Tayyip Erdogan's refusal to allow the central bank to raise interest rates to support the currency, as experts say it should. Erdogan has tightened his grip since consolidating power after general elections this year.