An American pastor imprisoned in Turkey is going on trial for alleged terror ties and spying in a case that has increased tensions between Washington and Ankara.

Andrew Craig Brunson, an evangelical pastor from North Carolina, is facing 35 years in prison on charges of "committing crimes on behalf of terror groups without being a member" and "espionage." The trial begins Monday in western Izmir province.

He was arrested in December 2016 for alleged links to both an outlawed Kurdish insurgent group and the network of the U.S.-based Muslim cleric who Turkey blames for a masterminding a failed military coup that year. The cleric, Fethullah Gulen, denies the claim.

Brunson has denied all allegations and maintains that he solely worked as a pastor

American officials have repeatedly requested that Brunson be released. In a meeting last year with his Turkish counterpart, President Donald Trump asked that the government "expeditiously" return the pastor to the U.S. But the appeals have not made much headway.

Turkish President Recep Tayyip Erdogan fired back at Washington in September, demanding that the U.S. first return Gulen.

"You give him to us and we'll give you this one," he said, referring to Brunson.

Turkey has submitted an extradition request to the U.S. for Gulen, who lives in Pennsylvania, but so far it not been granted — a point that festers in the Turkish government, which has hunted down tens of thousands of alleged Gulen supporters and either imprisoned them or fired them from government jobs.

Brunson, 50, has been living in Turkey for 23 years and served as the pastor of Izmir Resurrection Church with a small Protestant congregation. The pastor was first detained in October 2016 with his wife, Norine Brunson, who was later released.

The Izmir prosecutor's indictment against Brunson claims he was in contact with top-level executives of Gulen's network and the outlawed Kurdistan Workers' Party, or PKK. Both are designated terror groups in Turkey. Brunson is accused of acting in "parallel and coordinated fashion" with them, aiming to "divide" the country.

The prosecutor also accuses Brunson of espionage, saying Brunson acted "as an agent of unconventional warfare," gathering intelligence with religious work as his cover. The indictment — based on the testimonies of witnesses, including three secret ones, and alleged digital evidence — claims the pastor worked to convert Kurds to Christianity to sow discord.

The American Center for Law and Justice, a conservative Christian group in the U.S. lobbying for Brunson's release, has called him a "hostage of the Turkish government." A petition has garnered more than half a million signatures, stating that the case was putting Christianity on trial.