(CNN) Turkey's president lashed out at the US during a defiant speech Sunday, as the lira crumbled further following President Donald Trump's approval of higher tariffs and the threat of sanctions over an imprisoned pastor.

In the speech to supporters in the Black Sea city of Trabzon, President Recep Tayyip Erdogan said that his country would not acquiesce to US pressure, and that the Trump administration's actions were threatening the two countries' longstanding alliance.

"I want them to know that we will not surrender. We will keep producing and we will keep increasing exports," he said. "We will not give in... if you come at us with your dollars then we will find other ways to do business... The US is sacrificing its 81-million-strong ally Turkey for a pastor with links with terrorists."

Erdogan was referring to Andrew Brunson , a American evangelical pastor who Turkey accuses of helping to plot a 2016 coup attempt against the Turkish president. US officials maintain there is no credible evidence against Brunson, and the Trump administration has negotiated for weeks to secure his release.

On Friday, Trump a pproved a doubling of steel and aluminum tariffs on Turkey and warned that US relations with the country "are not good at this time." It was not immediately clear when the tariffs are due to take effect.

I have just authorized a doubling of Tariffs on Steel and Aluminum with respect to Turkey as their currency, the Turkish Lira, slides rapidly downward against our very strong Dollar! Aluminum will now be 20% and Steel 50%. Our relations with Turkey are not good at this time!

'Slaves to the dollar'

In his remarks Sunday, Erdogan said the US gave Turkey a deadline of last Wednesday to release Brunson or face further sanctions.

In revealing details of negotiations held between the two NATO allies, Erdogan said: "They are going to make us slaves to the dollar. Foreign exchange, interests... so what? They (US) said, 'if you don't release the pastor by 6 p.m. on Wednesday we will start sanctions.' They are going to sanction our interior and justice minister."

The United States slapped sanctions against Turkey's interior and justice ministers earlier this month, in response to Brunson's detention. Turkey responded by ordering the freezing of assets related to the US "justice and interior" secretaries.

The US State Department declined to comment on Turkey's allegations of a Wednesday deadline on the release of the American pastor.

In a New York Times opinion piece Friday, Erdogan said the decision to impose further sanctions "was unacceptable, irrational and ultimately detrimental to our longstanding friendship."

Held for two years

Brunson was arrested in Turkey in 2016 as the government launched a crackdown against perceived enemies in the wake of a failed military coup

He was formally indicted in March on charges of espionage and having links to terrorist organizations. The charges against Brunson include supporting the outlawed Kurdistan Workers' Party as well as the Gulen Movement, which Turkey says orchestrated the coup attempt.

He faces up to 35 years in prison if convicted. His trial is set to resume in October.

The American Center for Law and Justice (ACLJ) says that the charges are not legitimate and that Brunson was arrested primarily because of his Christian faith. US officials, including US Ambassador to Turkey John R. Bass, similarly said the accusations have no merit.

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Shifting allegiances?

In his speech Sunday Erdogan, repeated his accusation that the imposition of further tariffs by the US is tantamount to "economic warfare," and warned that the US stance could see a geopolitical shift in the NATO member's alliances.

Referencing Trump's imposition of tariffs on a host of global trading partners, including the EU, Canada and China, Erdogan said that it could force the country "towards new markets and new alliances."

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"Our response to those who wage a trade war against the whole world and include our country to that would be heading towards new markets and new alliances. Look at this, they increase tariffs on metal and steel. We are a member of World Trade Organization. This is not among the rules of World Trade Organization."

The remarks were a reiteration of Friday's Times op-ed, in which Erdogan said that the US' "failure to reverse this trend of unilateralism and disrespect will require us to start looking for new friends and allies."

In an opinion piece Sunday , CNN National Security Analyst Samantha Vinograd wrote that Turkey's being a NATO member "hasn't stopped (Erdogan) from cozying up to Russian President Vladimir Putin and buying defense assets from him (a US sanctions violation) or voicing contentment over Russia and Turkey's ongoing cooperation in the energy and defense industry sectors during a conveniently timed phone call on Friday.

"Erdogan is likely trying to publicly signal he could go over to the dark side, aka the anti-NATO, Putin side. We should also expect Turkey to draw even closer to Iran."

Freefall

The dispute has caused the lira to go into freefall , with the Turkish currency losing a fifth of its value to the dollar in the last week. The currency had already been underperforming before the current spat -- it has dropped almost 40% against the dollar this year.

On Friday, Erdogan urged the Turkish people to exchange dollars and euros for lira in order to defend the currency.

However, the currency fell again Monday as fears deepened about the country's ability to deal with a crisis that has rattled markets around the world, dropping as much as 11% against the dollar in morning trading in Asia.

Investors are anxious about the political clash with the United States intensified and the Turkish government's lack of measures to tackle the problems plaguing its economy.

Erdogan is ignoring calls to increase interest rates, but economists are warning that if confidence isn't restored quickly, Turkey could lurch into a recession and debt crisis requiring a bailout from the International Monetary Fund.

"Investors are clearly concerned that Turkey's government won't act (or allow the central bank to act) to shore up the currency, and fears are mounting that this could result in a crisis in Turkey's banking sector," William Jackson, chief emerging markets economist at research firm Capital Economics, wrote in a note to clients Friday.