U.S. Secretary of State Mike Pompeo has called for the release of American Pastor Andrew Brunson when he spoke to Turkish Foreign Minister Mevlut Cavusoglu on Friday.

A U.S. official told reporters that Pompeo, who was recently confirmed as the U.S. Secretary of State on Thursday, brought up Brunson's plight when he talked with Cavusoglu during the NATO ministerial meeting in Brussels, Belgium.

"Secretary Pompeo reiterated the concerns we have for U.S. citizens and consular staff detained in Turkey and especially Pastor Brunson," the U.S. official said, according to Voice of America.

Heather Nauert, the acting U.S. Under Secretary of State for Public Diplomacy, noted that the Cavusoglu and Pompeo also discussed the situation in Syria as well as the U.S.-Turkey partnership in the region.

Brunson, who led a small church in Izmir for over 20 years, has been incarcerated in Turkey for 18 months over allegations of terrorism and espionage. If convicted, he could face up to 35 years in prison.

The charges against Brunson were reportedly based on the testimonies of a secret witness. The indictment against the pastor alleged that he had a hand in organizing the July 2016 coup against Turkish President Recep Tayyip Erdogan. He was also accused of being in possession of secret documents related to the goal of overthrowing the government.

The pastor denied all the allegations during the first hearing of his trial in April. "I don't accept any of the allegations or accusations," Brunson said, according to The Stream.

"I did not engage in any illegal activity. I had no relations with anyone engaged in such activity. I am a Christian pastor. I did not join an Islamic movement. Their aims and mine are different," he added.

Brunson's next hearing is expected to take place on May 7, 2018.

U.S. President Donald Trump has expressed support for the pastor and denounced the Turkish government for prosecuting him as a spy.

"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!" the U.S. president said in a tweet in April.

Meanwhile, Erdogan suggested that Brunson can be released if the U.S. decides to extradite Islamic cleric Fethullah Gulen, who is being blamed by the Turkish government for instigating the 2016 coup. The U.S., however, has refused to hand over the cleric, who is currently living in Pennsylvania, due to lack of evidence.