The lawyer for US evangelical pastor Andrew Brunson said he filed an appeal on Wednesday to Turkey's constitutional court for his client's release from house arrest.

The case of Andrew Brunson, whose next regular court hearing is on October 12, has become the most divisive issue in a worsening diplomatic row between Ankara and Washington that has triggered US sanctions and tariffs against Turkey.

The filing to the constitutional court – Turkey's highest – seen by Reuters showed the lawyer had requested the court to rule that Brunson's right to freedom had been violated and to release him from house arrest.

State Department spokeswoman Heather Nauert told a news conference on Tuesday that the United States would maintain close contact with the Turkish government over Brunson's trial.

'We certainly would like Pastor Brunson home right away. It's long overdue,' she said.

Brunson is charged with links to Kurdish militants and supporters of Fethullah Gulen, the cleric blamed by Turkey for a failed coup attempt in 2016. He has denied the accusation – as has Gulen – and Washington has demanded his immediate release.

Jailed or held under house arrest since October 2016, Brunson faces up to 35 years in jail if convicted. Last month the main prosecutor in his trial was replaced, a move which his lawyer cautiously welcomed, saying it might be a sign of changing political will.

President Tayyip Erdogan has said politicians have no sway on the judiciary and that the courts will decide on Brunson's fate. He said on Monday that Brunson has 'dark links with terror organisations'.