(CNN) The Trump administration's threats to issue economic sanctions against Turkey late last week rapidly escalated increasing tensions between the two countries.

And at the center of this international incident is one man: a detained American pastor named Andrew Brunson

To Turkey, Brunson is a spy who attempted to overthrow the government during a 2016 coup attempt. But to US officials, Brunson is an innocent Christian family man who is being wrongfully detained.

The debate has strained relations between the NATO allies and raised the possibility of significant sanctions and further threats. So who exactly is Brunson, and how did the pastor become a key figure in US-Turkey relations?

Evangelical Presbyterian pastor

Brunson, 50, is a native of North Carolina and an evangelical Presbyterian pastor who worked in Izmir on Turkey's Aegean coast, where he was a pastor at the Izmir Resurrection Church.

He has lived in Turkey for more than 23 years with his wife and three children, according to the American Center for Law and Justice (ACLJ), an organization led by attorney Jay Sekulow that has advocated for his release.

But in October 2016, several months after a failed coup attempt in Turkey, Brunson was arrested and accused of plotting to overthrow the Turkish government.

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.

US President Donald Trump has called for the release of Andrew Brunson, right, an American pastor who has been detained in Turkey.

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

The 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.

"He appears to be being held simply because he's an American citizen who as a man of faith was in contact with a range of people in this country who he was trying to help, in keeping with his faith," Bass said in October 2017

Turkey released Brunson to house arrest on Wednesday and ordered him to wear an electronic monitoring device. State-run news agency Anadolu reports the Turkish court decision was due to his "health problems."

Several US officials praised the release to house arrest but maintain that he should be fully released.

"We have seen no credible evidence against Mr. Brunson, and call on Turkish authorities to resolve his case immediately in a transparent and fair manner," Secretary of State Mike Pompeo said last week.

Trump administration threatens sanctions

Even before last week's move to house arrest, the White House has repeatedly pushed for Brunson's release in conversations with Turkish officials. That push has since escalated to threats of economic sanctions.

Trump has tweeted about Brunson three separate times from his personal account, including twice in the past two weeks. The first of those came in April, when Trump tweeted that Brunson was being "persecuted in Turkey for no reason."

"They call him a Spy, but I am more a Spy than he is. Hopefully he will be allowed to come home to his beautiful family where he belongs!"

Pastor Andrew Brunson, a fine gentleman and Christian leader in the United States, is on trial and being persecuted in Turkey for no reason. They call him a Spy, but I am more a Spy than he is. Hopefully he will be allowed to come home to his beautiful family where he belongs! — Donald J. Trump (@realDonaldTrump) April 18, 2018

On July 18, Trump said it was a "total disgrace" that Turkey won't release Brunson, he wrote in a tweet that tagged Erdogan's account.

"A total disgrace that Turkey will not release a respected U.S. Pastor, Andrew Brunson, from prison. He has been held hostage far too long," Trump said.

Finally, on Thursday, Trump tweeted that the US will impose "large sanctions" on Turkey for their detainment of Brunson, "a great Christian family man and wonderful human being. He is suffering greatly. This innocent man of faith should be released immediately!"

Vice President Mike Pence similarly said that the US will impose "significant sanctions" on Turkey until Brunson is released.

"I know that his faith will sustain him, but it shouldn't have to," Pence said at the Ministerial to Advance Religious Freedom. "Pastor Andrew Brunson deserves to be free."

Andrew Brunson, center, is seen inside a car escorted by Turkish plain-clothes police officers as he arrives at his house in Izmir on July 25.

Turkish officials have sharply criticized the US threats of sanctions.

"No one dictates Turkey. We will never tolerate threats from anybody. Rule of law is for everyone; no exception," Turkey's Foreign Minister Mevlut Cavusoglu said on his official Twitter account Thursday.

Hami Aksoy, the spokesperson of Turkey's Ministry of Foreign Affairs, said the threats were "unacceptable." and disregarded the US-Turkey alliance.

"It is impossible to accept the U.S. Administration's threatening messages, which totally disregard our alliance and friendly relations between our countries," Aksoy said.

Pompeo said Friday that he spoke with Cavusoglu and "underscored that it is well past time for this innocent Pastor Andrew Brunson to come home."

I spoke yesterday with Turkey's Foreign Minister @MevlutCavusoglu and underscored that it is well past time for this innocent Pastor Andrew Brunson to come home. pic.twitter.com/6zU8pw0P0A — Secretary Pompeo (@SecPompeo) July 27, 2018

Possible prisoner swap

Although Turkish President Recep Tayyip Erdogan has said that Brunson "is not a hostage," he has made comments raising the possibility of a prisoner swap for Brunson.

Erdogan in May questioned why the US was asking for Brunson's release even as the US refused to extradite Fethullah Gulen. Gulen is an exiled cleric living in Pennsylvania whom the Turkish government accuses of being behind the failed coup attempt.

"(Gulen's) being harbored there. And he's not a convict. He's not even being detained," Erdogan said. "And we demand his extradition, and he's not being extradited to us. But there is a Pastor Brunson here, who is being currently prosecuted -- and he's allegedly associated with terrorist organizations. And you're asking for him?"

Last fall, Erdogan raised Gulen's extradition in a televised speech that suggested Gulen and Brunson could be swapped.

"'Give us the pastor back,' they say. Well, you have a pastor as well. Give that one back to us, then we will give (Brunson) back to you," Erdogan said.

Erdogan's comments "created the perception that Brunson was illegally arrested as a bargaining chip," according to Fadi Hakura, who manages the Turkey Project at Chatham House in London.

Brunson's release to house arrest on Wednesday came after Trump asked Israeli Prime Minister Benjamin Netanyahu to assist in his release, Israeli and US officials told CNN.

A senior US official told CNN that in exchange for Turkey's release of Brunson, Israel agreed to release Ebru Ozkan, a 27-year-old Turkish woman held in Israel on suspicion of aiding Hamas, the Palestinian militant group that controls Gaza.

Ozkan was released from prison between July 11 and 12, a lawyer for Ozkan told CNN. She was able to leave Israel for Turkey on July 15, one day after Trump spoke with Netanyahu.

Erdogan denied on Sunday reports that Brunson was released in exchange for allowing Ozkan to leave Israel.

"We told the Americans that they could help us with getting Ebru. ... But we never said: 'and in exchange we will give you Brunson,'" Erdogan said, according to state broadcaster TRT.