Turkey’s president has warned the US that it will lose a valuable ally unless it changes its approach to the case of an American held in Turkey on espionage charges. Washington is threatening Ankara with sanctions over the issue, RT reported.

Talking to Turkish media about US threats of sanctions if Ankara doesn't release Pastor Andrew Brunson, Recep Tayyip Erdoğan said US president Donald Trump is waging a "psychological war," the Daily Sabah reports.

Washington would lose a "strong and sincere ally" if the administration there does not change its attitude regarding Brunson, Recep Tayyip Erdoğan said, after Trump threatened to impose sanctions against its NATO ally. 

"The United States will impose large sanctions on Turkey for their long time detainment of Pastor Andrew Brunson, a great Christian, family man and wonderful human being. He is suffering greatly. This innocent man of faith should be released immediately!" Trump wrote on Twitter.

Pastor Andrew Brunson, who has lived in Turkey for over twenty years, is currently being held on charges of supporting a group that Ankara says was behind the failed military coup in 2016. The pastor, who maintains his innocence, faces up to 35 years in jail if found guilty.