The sister of Andrew Brunson, the American missionary jailed in Turkey on what his supporters say are false charges of membership of a terrorist organisation, has spoken of how the family's faith in God is sustaining them.

Beth Herman told Breitbart News: 'It's been very hard on us as his family. We love him and we want him to be back with his family.'

She said her brother 'loves the Turkish people and he's tried to do only good to them', adding he would 'do nothing that would hurt anybody'.

'We have a strong faith in God,' Herman said. 'We believe God is with him and he'll make it through this.'

Brunson and his wife Norine ran a small church in Izmir and were initially held on immigration charges. Norine was released but the charge against Andrew Brunson was scaled up and he was accused of being a supporter of Fethullah Gulen, a US-based Muslim cleric blamed – wrongly, many observers say – for a failed coup last July.

Turkey's President Recep Tayyip Erdogan launched a programme of fierce repression after the coup attemp, jailing thousands of people and firing many from government positions. A referendum later this month may see him granted even more sweeping powers.

Brunson has asked the US government to intervene for him with Erdogan, writing from his cell a fortnight ago: 'I plead with my government – with the Trump Administration – to fight for me.'

He added: 'Will the Turkish government face no consequence for stubbornly continuing to hold an American citizen as a political prisoner?''

Brunson said: '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.'