Turkey President Recep Tayyip Erdogan warned the U.S. not to impose sanctions against his government over the ongoing imprisonment of an American pastor accused of espionage and terror-related charges.

Andrew Craig Brunson, 50, was arrested in December 2016 and held in a Turkish prison until he was released to home detention last week. The pastor, who is originally from Black Mountain, N.C., has lived in Turkey for 23 years and led Izmir Resurrection Church.

Late Saturday, Turkish media quoted Erdogan as saying that Washington "cannot make Turkey back down with sanctions."

"The U.S. should not forget that unless it changes its attitude, it will lose a strong and sincere partner like Turkey," warned Erdogan, who is on an official visit to southern Africa this week.

Brunson was detained in the aftermath of a failed 2016 coup on charges of "committing crimes on behalf of terror groups without being a member" and espionage. His He faces a prison sentence of up to 35 years if he is convicted on both counts at the end of his ongoing trial.

On Thursday, President Trump announced possible sanctions against Turkey -- a member of NATO -- over its treatment of Brunson. On Sunday, Vice President Mike Pence told Fox Business Network's "Sunday Morning Futures" that Brunson's release to house arrest "is just not good enough."

"Pastor Andrew Brunson is an innocent man. He’s a man of profound Christian faith, who has ministered in Turkey for more than 20 years ... There's no credible evidence of any wrongdoing against him," Pence said. "The United States of America is prepared to bring sanctions against Turkey until Pastor Andrew Brunson is free."

Erdogan denied speculation that there had been an agreement to swap Brunson for Turkish citizens being held abroad, particularly 27-year-old Ebru Ozkan. Ozkan had been detained by Israel on terror-related charges, but was deported this month.

The Turkish leader previously linked Brunson's return to the U.S. to the extradition of Fethullah Gulen. Ankara blames Gulen for the coup attempt, while the cleric denies involvement.

Erdogan also warned that Turkey would seek international arbitration if the United States refused to deliver F-35 fighter jets in retaliation.

The Associated Press contributed to this report.