YENISAKRAN, Turkey — A Turkish court on Monday ordered an American pastor to remain behind bars as his trial for opened on charges that he aided terrorist groups in Turkey.
The pastor, Andrew Brunson, 50, who has worked in Turkey as a missionary for 23 years, has been detained for 18 months. He was arrested in the aftermath of the failed coup against President Recep Tayyip Erdogan in 2016, and American officials have been unsuccessful in their efforts to secure his release.
Mr. Brunson, leader of the Resurrection Church in the seaside city of Izmir, stands accused of aiding the Kurdistan Workers’ Party, the P.K.K., which has been waging a separatist insurgency inside Turkey for three decades. He is also accused of having links to followers of Fethullah Gulen, an Islamist preacher who lives in Pennsylvania and who Turkey claims masterminded the coup attempt.
In an emotional appeal to the court on Monday, Mr. Brunson said he had suffered a breakdown in jail, stopped eating and lost weight. He begged to be sent home under house arrest, but the judge upheld a judicial order last week that the pastor remain incarcerated for another month. Family and friends present for the proceeding had been hoping that Mr. Brunson would be freed now that his trial has finally begun.
The case has drawn high-level interest in the United States. Both President Trump and Vice President Mike Pence have raised it in meetings with Turkish officials, and on Monday Senator Thom Tillis of North Carolina, Mr. Brunson’s home state, was present for the trial. So was Sam Brownback, a former senator and governor from Kansas whom Mr. Trump recently appointed as ambassador at large for international religious freedom.
Mr. Brownback said the American government had looked into his case and was convinced that Mr. Brunson was innocent.
“People are deeply concerned and focused and interested in this case,” he said. “The administration and the United States cares deeply about our relationship with Turkey. This is a valuable ally of ours and we deeply value our relationship. We want to see this resolved.”
Mr. Tillis said the case was not being tied to Turkey’s request for the extradition of Mr. Gulen, or the discussions over American support for the Kurdish-led militia in Syria.
“There should not be a linkage here,” Mr. Tillis said. “This is about what we believe is an innocent man who has been imprisoned for over a year and a half, and we are encouraging his release and back to a positive dialogue between the United States and Turkey.”
In a signal of some softening in the relationship between the United States and Turkey, American prosecutors have dropped charges against Mr. Erdogan’s bodyguards who were accused of assault after clashing with protesters in Washington in May last year.
Mr. Brunson faces far more serious charges. In a trend that has followed the coup attempt of July 2016, he has been accused of aiding followers of Mr. Gulen’s movement and the Kurdish P.K.K. without being a member of either organization.
The evidence was presented in court partly by two anonymous witnesses who gave testimony by video that distorted their images and voices.
Mr. Brunson categorically denied accusations that he had encouraged Kurdish separatist sentiment in his church and that he had held meetings to support terrorist groups and their aims under the cover of humanitarian and missionary work.
“I’ve never done anything against Turkey,” he told the court. “I love Turkey. I’ve been praying for Turkey for 25 years. I want truth to come out.”
Mr. Brunson denied any connection to Mr. Gulen and said he had returned from vacation in the United States after the coup when others were fleeing the country — proof, he said, that he had no connection to the movement.
He also denied that his work with Syrian and Kurdish refugees meant that he supported Kurdish separatism. “What is being shown here is my service and it is called a cover,” he told the court. “It is my spiritual services.”
“I talk about Jesus but it is not to support the P.K.K.” Mr. Brunson said. “It is not to convert them to Christianity and be against Turkey. I say the same to Turks. I am not interested in politics. I’m not in favor of separation. I believe in Turkey’s integrity. What else can I say?”
Among Mr. Brunson’s supporters was Ihsan Ozbek, chairman of the Association of Protestant Churches in Turkey, a fellow pastor who dismissed the trial. “It’s an empty case,” he said.
An American supporter, William Devlin, co-pastor of the Infinity Bible Church in the South Bronx, said he had traveled to Turkey to offer to take the place of Mr. Brunson in prison.
“He is here to serve the people of Turkey and the Christian faith,” he said. “He has been here for 23 years and he is innocent.”