Image copyright Reuters Image caption Andrew Brunson (third right) denies links to banned groups in Turkey 
 
 The US is increasing pressure on Turkey to try to secure the freedom of American pastor Andrew Brunson. While the leaders of the two Nato allies clash with each other, Mr Brunson's fate hangs in the balance. 
 
 US President Donald Trump tweeted earlier this week that Mr Brunson was being held "hostage" in Turkey. Mr Brunson should be released, he said. 
 
 Mr Brunson has been held for almost two years because of his alleged links to political groups that are outlawed in Turkey and he is now under house arrest. Members of the Protestant evangelical church in the US - part of the president's base of support - have rallied on his behalf, demanding his freedom. 
 
 Mr Trump and his aides have amplified their demands and criticised the actions of President Recep Tayyip Erdogan. A senior US official has wondered aloud whether Turkey could even be considered a true Nato ally, given how Turkish officials have treated Mr Brunson. 
 
 "A real Nato ally wouldn't have arrested Brunson in the first place," the official said. 
 
 Mr Trump and Mr Erdogan, says the Center for Strategic and International Studies' Jon Alterman, are in a personal feud - with Mr Brunson as a "pawn". 
 
 Mr Brunson, 50, is originally from Black Mountain, North Carolina, and he runs a small evangelical church in Izmir, Turkey. He has denied any wrongdoing. 
 
 US officials have imposed financial sanctions against Turkey and called for Mr Brunson's release. Turkish officials say they won't cave in to threats from the US. 
 
 Officials from the US and Turkey have imposed tariffs on one another's goods. The conflict between the two countries has aggravated Turkey's economic crisis - the lira has lost about a third of its value against the dollar since January. 
 
 And now US officials are threatening to retaliate against Turkey even more. 
 
 Image copyright AFP Image caption Trump and Erdogan are divided on a number of issues 
 
 Senior US officials are discussing additional sanctions that could be imposed. US Treasury Secretary Steven Mnuchin said that they had more in mind - and could be put into effect if Mr Brunson was not freed. 
 
 US officials have also said that further negotiations over a contentious issue in US-Turkish relations - a Turkish state bank, Halkbank, which allegedly helped Iran to evade US sanctions - will have to wait until Mr Brunson is released. 
 
 US treasury department officials have subpoenaed the bank, according to a US official, and received material from them. But at this point the US officials are unsatisfied with the material that Halkbank has provided. 
 
 In addition, according to a US official, the US justice department is pursuing an investigation into Halkbank and the case, the US official warned, could turn into a criminal one. 
 
 Turkish officials have said the bank did nothing illegal and shouldn't be penalised. 
 
 Meanwhile the feud continues. Mr Trump wants Mr Erdogan to release Mr Brunson for humanitarian reasons. If Mr Brunson is found guilty, he could face up to 35 years in prison. 
 
 But there are other reasons too, says Joshua Landis, a professor of Middle East studies at the University of Oklahoma in Norman. He says that if Mr Trump wins Mr Brunson's freedom, then the president can claim that his "strong-arm tactics" are effective in the realm of foreign policy. 
 
 Besides that, says Mr Landis, securing the release of Mr Brunson would be welcomed by "the religious right". 
 
 "That's his bread and butter," says Mr Landis. "He's doing this for them." ||||| Image copyright Getty Images Image caption Pastor Andrew Brunson was moved to house arrest last month due to health issues 
 
 The US has imposed sanctions on Turkey's justice and interior ministers over the continued detention of American pastor Andrew Brunson. 
 
 The evangelical from North Carolina has been held for nearly two years over alleged links to political groups. 
 
 "We believe he's a victim of unfair and unjust detention," White House press secretary Sarah Sanders said. 
 
 Turkey has said US demands for Mr Brunson's release are "unacceptable", adding it will respond to "hostility". 
 
 "We call on the US administration to row back from this wrong decision," the Turkish foreign ministry said in a statement on Wednesday. 
 
 "Without delay, there will be a response to this aggressive attitude that will not serve any purpose," it continued. 
 
 The US Treasury Department later said Turkey's Justice Minister Abdulhamit Gul and Interior Minister Suleyman Soylu were targeted because they "serve as leaders of Turkish government organizations responsible for implementing Turkey's serious human rights abuses". 
 
 'Nato allies at each other's throats' 
 
 Image copyright Reuters Image caption Presidents Trump and Erdogan met at a Nato summit in Brussels last month 
 
 By Mark Lowen, BBC Turkey correspondent 
 
 It is unprecedented for the US to hit a Nato ally with sanctions. The relationship has plunged to its lowest level in decades. 
 
 But it is remarkable to think that in 2016, Turkey's government was gunning for a Donald Trump victory. Michael Flynn, Mr Trump's disgraced former national security advisor, was paid to lobby for Turkey in Washington. There was confidence that presidents Trump and Recep Tayyip Erdogan could form a strongman partnership to reset ties. 
 
 President Erdogan is known for lashing out at Western leaders. He hasn't taken kindly to being the one browbeaten by the US. 
 
 Pro-government columnists are calling for the US military base here to be shut down. A crucial security partnership is at risk with two Nato allies at each other's throats. 
 
 Meanwhile, Turks are suffering as the lira reaches new lows. Erdogan critics say he should have been sanctioned long ago - over mass arrests, human rights violations and buying a missile defence system from Russia. But now sanctions have come, the fear is of what two unpredictable leaders will do next. 
 
 Speaking to reporters, Sarah Sanders said: "We've seen no evidence that Pastor Brunson has done anything wrong." 
 
 She added that the two Turkish ministers had both played "leading roles" in the arrest of the US pastor. 
 
 "As a result, any property or interest in property of both ministers within US jurisdiction is blocked and US persons are generally prohibited from engaging in transactions with them," she said. 
 
 Ms Sanders also said that President Trump had discussed the matter with President Erdogan "multiple times". 
 
 Last week, President Trump warned Turkey it would face "large sanctions" if it did not release Mr Brunson immediately. 
 
 Following Wednesday's announcement, the Turkish lira lost 1.6% of its value to fall to 5.0 against the US dollar. 
 
 Who is Andrew Brunson? 
 
 Mr Brunson is a long-term resident in Turkey. He lived with his wife and three children while working as the pastor of the small Izmir Resurrection Church, which had a congregation of about two dozen. 
 
 The authorities accuse him of having links with the outlawed Kurdistan Workers' Party (PKK) and the Gulenist movement, which Turkey blames for a 2016 failed coup. 
 
 Image copyright Reuters Image caption Turkey has urged the US to extradite Muslim cleric Fethullah Gulen 
 
 Mr Brunson has denied charges of espionage, but faces up to 35 years in jail if found guilty. 
 
 He was moved into house arrest last month for health reasons, but US Secretary of State Mike Pompeo said this was not enough. 
 
 "We have seen no credible evidence against Mr Brunson," Mr Pompeo tweeted at the time. 
 
 Turkey's foreign ministry said it had shared "necessary information" with the US, but insisted the case should be left with its judiciary. 
 
 What is Turkey's motivation? 
 
 Mr Brunson is one of 20 Americans who were charged after the coup two years ago, according to the New York Times. 
 
 More than 50,000 people were arrested in Turkey in President Erdogan's huge post-coup crackdown. 
 
 He blames Pennsylvania-based Muslim cleric Fethullah Gulen for the attempt, but Mr Gulen denies any involvement. 
 
 Turkey wants the US to agree to his extradition. Mr Erdogan has indicated he would swap the pastor for "the priest" (Mr Gulen). 
 
 US support for Kurdish forces fighting the Syrian civil war has also angered Mr Erdogan, who views them as an extension of the PKK. 
 
 The PKK - a Turkish-Kurdish rebel group fighting for autonomy since the 1980s - is considered a terrorist group by Turkey and the US.
– The disagreement with the US currently devastating the Turkish economy doesn't appear likely to end anytime soon. American pastor Andrew Brunson, who was jailed by Turkey for almost two years before a shift to house arrest last month, is at the center of the dispute and a senior White House official tells the Wall Street Journal that the US has rejected a Turkish offer to trade his freedom for dropping charges against Halkbank, a state-owned bank facing billions in US fines for violating sanctions on Iran. The US has told Turkey it won't negotiate until Brunson, who faces up to 35 years in prison if convicted, is freed, the White House official says, adding: "A real NATO ally wouldn’t have arrested Brunson in the first place." The US has already hit Turkish officials with sanctions over Brunson and the two countries have traded tariff increases, causing the Turkish lira to plummet to record lows. Brunson, a pastor from North Carolina strongly supported by American evangelical groups, was arrested because of his alleged ties to banned political groups, the BBC reports. American officials have threatened even more sanctions unless Brunson is freed, while Turkey has said it will not give in to American threats. Jon Alterman at the Center for Strategic and International Studies describes Brunson as a "pawn" in a feud between President Trump and Turkey's President Recep Tayyip Erdogan. (Shots were fired at the US Embassy in Ankara early Monday.)