An American missionary jailed in Turkey is pleading with President Trump to secure his release.

Andrew Brunson has been detained since October when he and his wife were held on immigration violation charges after running a small church in Izmir, on Turkey's western coast.

'I plead with my government – with the Trump Administration – to fight for me,' he wrote from his jail days before Secretary of State Rex Tillerson is due to meet Turkish President Recep Tayyip Erdogan.

Published by the American Center for Law and Justice, an advocacy group backing the pastor, the letter was passed US embassy officials after a meeting on Wednesday.

'Will the Turkish government face no consequence for stubbornly continuing to hold an American citizen as a political prisoner?' writes Brunson.

'Even though I have a long public track record as a church pastor, they falsely accuse me of being a member of an Islamist terrorist group.'

Although Brunson's wife has been released, his charges have been scaled up and he now faces accusations of terrorism.

The Turkish government have produced no evidence of their claims but prosecutors have suggested he is being held on suspicion of links to Fethullah Gulen, a US-based Muslim cleric blamed for a failed coup last July.

President Erdogan has labelled Gulen a terrorist and asked both the Trump and Obama administrations to deport Gulen to face trial in Turkey.

Tillerson will meet the Turkish president in Ankara on Thursday and Gulen will certainly be discussed amid tensions over the US military action in Syria and alliance with Kurdish forces.

Brunson went on: 'I have been imprisoned since October 7, 2016. During this time the Turkish government has produced no proof and has rebuffed numerous attempts by the American government to secure my return to the United States.

'In fact they are treating the US government with contempt and paying no price for it.'

The ACLJ backed Brunson's call and called on Tillerson to step in. 

'The US government must take a more active role in fighting for Pastor Andrew's release,' a statement on Wednesday read. 'He has done nothing wrong. He is a US citizen wrongfully imprisoned in a foreign land because of his Christian faith. He deserves to be free.'