Turkish President Recep Tayyip Erdogan says the United States is seeking to stab Turkey “in the back”, as Washington has slapped Ankara with “large” sanctions over the detention of an American pastor on terror-related charges, triggering unprecedented tensions between the two NATO allies.

“You act on one side as a strategic partner but on the other you fire bullets into the foot of your strategic partner,” Erdogan told a conference in the capital Ankara on Monday, addressing his US counterpart Donald Trump.

“We are together in NATO and then you seek to stab your strategic partner in the back. Can such a thing be accepted?” Erdogan asked.

His comments came as relations between Washington and Ankara have taken a turn for the worse amid bitter dispute over the detention in Turkey of American evangelical pastor Andrew Brunson on terrorism charges. The growing rift has also sent the Turkish lira into a tailspin.

Trump wrote on Twitter late last month that his country “will impose large sanctions on Turkey for their long time detainment of Pastor Andrew Brunson.” He also said on Friday that he had ordered to double US tariffs on Turkish aluminum and steel imports to 20 percent and 50 percent, respectively.

Trump’s announcement came shortly after Erdogan called on Turks to help defend the country against the US-launched economic war against his nation. He also appealed to Turks to exchange dollars and gold for Turkish lira to support the plunging currency.

Defying US pressures, Ankara now says it is ready to take all necessary measures to ensure financial stability, as lira has been in the free fall since Friday.

The Turkish leader also said his nation was facing an “economic siege”, denouncing the currency movements as an “attack against our country.”

In a bid to allay Turks’ financial concerns, Erdogan further said, “It is not at all like we sank and we are finished. The dynamics of the Turkish economy are solid, strong and sound and will continue to be so.”

On Saturday, Erdogan warned his country’s partnership with the US might be in “jeopardy” as tensions intensify between the sides.

Meanwhile, Turkish Foreign Minister Mevlut Cavusoglu called on the US administration to be a “faithful friend and NATO ally.” “We are open to diplomacy and consensus but it is impossible to accept any imposition,” he added.

Ankara and Washington also disagree over their military interventions in the Syria war, Turkey’s plan to buy missile defense systems from Russia and the US conviction of a Turkish state bank executive on sanctions-busting charges in January.