“We will pay nothing for the release of an innocent man, but we are cutting back on Turkey!” a tweet from the president late on Thursday said.
On Friday, Turkey threatened further action if the US followed through on several promises to levy heavy sanctions unless Mr Brunson was released.
The lira plummeted to just 5.8 against the dollar and 6.7 against the euro on Friday, compared to just over seven to the dollar a few days earlier. It has lost 40 per cent of its value since the beginning of the year.
The Turkish ambassador to the US met with Mr Trump’s national security advisor John Bolton earlier this week, Reuters reported, and offered to tie conditions to Mr Brunson’s release.
Mr Bolton reportedly dismissed the offer.
“[Turkey] missed a big opportunity. This is very easy to resolve,” an unnamed US administration official said. “They made a big mistake trying to tie this to other things.”
Mr Trump’s new warning comes on top of remarks from Steven Mnuchin, the US treasury secretary, who suggested at a cabinet meeting on Thursday another round of tit-for-tat sanctions was imminent.
“They have not proven to be a good friend,” Mr Trump said of Turkey during the meeting. “They have a great Christian pastor there. He’s an innocent man.”
Mr Brunson, an evangelical pastor and American citizen who has lived in Turkey for decades, was detained in Izmir in October 2016 on terror-related charges after the failed July military coup.
More than 50,000 people remain in prison facing allegations of involvement in the coup, which led to a two-year state of emergency and a crackdown on opposition to president Recep Tayyip Erdogan.
Ties between Ankara and Washington have also soured over Turkey’s state-owned Halkbank, which the US says should be fined for allegedly helping Iran evade US sanctions, and Turkey’s unfulfilled demand that the US extradite Turkish cleric Fethullah Gulen, whom Turkish authorities hold responsible for the 2016 coup.
Last week, Mr Trump tweeted that his administration was sanctioning two Turkish officials and doubling aluminium and steel tariffs for Turkey.
Ankara responded by imposing $533m (£420m) of tariffs on US imports such as cars, tobacco and alcohol and a boycott of US electronics, singling out iPhones.