May 2022 marks 20 years since strict rules on religious freedoms forced Eritrean churches to shut their doors, with non-Orthodox Christians forced to renounce their faith or face imprisonment.
Last month, 29 Christians were arrested when gathering for prayer in a private home; they have since been imprisoned.
Andrew Boyd, from Release International, says that the prisons are "beyond description", with believers branded "enemies of the state."
He said: The prisons are appalling, overcrowded, horrible places, but some of the Christians have been kept in shipping containers in the desert.
"Eritrea is a blindingly hot country... if you can imagine being kept in a tin box, in the desert in the day, almost too hot to touch, unsanitary, unventilated.
"Then at night, freezing cold and beaten to try to get you to renounce your faith.
"Absolutely awful."
Despite the unimaginable conditions that many followers are facing, Andrew says the spirit of Christ is still alive within the "tin box" shipping containers:
"Jesus said in the Bible we would be persecuted.
"He said 'If they hate me, they hate you also.'
"We're called to reverse that hatred with love. That's why we're told to pray for the persecutors and the Christians in Eritrea do that, even those who are being tortured do it.
"There's one remarkable example of somebody who's in prison within a shipping container. Helen was so brutally tortured she couldn't bear anymore, but she was being called out again to be tortured and another Christian decided to take her place and take that punishment.
"That's a clear reference to what Jesus did for us when he was crucified on the cross, and as we stand with these people, hold them in our hearts and pray. It's not about being weighed down by it, but it is choosing to care.
"It's choosing to love and when we pray, we're putting love and action. That's what prayer is."