President Donald Trump doubled tariffs on Turkish metals exports to the United States last week prompting Turkey, which says it will not bow to threats, to raise tariffs on U.S. cars, alcohol and tobacco by the same amount on Wednesday.
"We have more that we're planning to do if they don't release him quickly", Mnuchin told a cabinet meeting, without elaborating on what would be involved.
He faces 35 years in prison on espionage and terror-related charges.
While Erdogan has said Turkey would respond to the sanctions by boycotting USA goods, Aljazerra reported Foreign Minister Mevlut Cavusoglu is sending a more positive message but cautioned about the Trump administration on its tone in future negotiations.
Mr Trump said: "They want to hold our wonderful pastor".
"It nearly seems as if Trump's words were an invitation for there to be even more of an entrenchment of this dispute", said Al Jazeera's Sonia Gallego, reporting from Turkey's largest city of Istanbul. The crisis has been precipitated by investor alarm about President Tayyip Erdogan's influence over monetary policy.
Turkey unlikely to give up on U.S. despite unprecedented row
Turkey said Wednesday it was imposing extra tariffs on imports of products, including rice, vehicles, alcohol, coal and cosmetics. But the Turkish government's framing of its problems as an epic battle for sovereignty against outside enemies, particularly U.S.
Erdogan: Turkey can do without U.S. electronic goods
But the lira posted gains on forex markets for the first time after days of losses, giving the currency much needed respite. President Recep Tayyip Erdogan suggested that Turkey will stick to Samsung and Vestel if United States products are banned.
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Last week, President Trump authorized doubling tariffs on Turkish steel and aluminum which has further strained economic tensions with Turkey. "We are not going to take this sitting down". It hit an all-time low of 7.2 lira to the dollar earlier in the week.
Whatever action the United States does take, economists said it looked likely to cause more pain for Turkish assets in the immediate future.
The issue has led to a dramatic souring of U.S. -Turkey relations. The lira's sharp decline has sparked fears in the worldwide community of a Turkish economic crisis.
The dispute over Brunson and other frictions between Washington and Ankara have been one reason the Turkish lira has plunged 40 per cent this year.
He says the USA will pay nothing for his return, because he is innocent and indicated the pressure on Turkey will continue.
Mr Trump's comments came as Turkey's finance minister Berat Albayrak attempted to reassure 6,000 worldwide investors and economists on a video link that the country would emerge stronger from the crisis.
Investors are concerned that Turkey has amassed high levels of foreign debt to fuel growth in recent years.