Afghans suspected of being Christians are at risk of being killed "immediately" by the Taliban if they refuse to renounce the faith.
The warning came from Christian satellite channel SAT-7, which says it has seen a surge in calls to its counselling phone line from Afghans "desperate for encouragement and hope" after the chaotic takeover by the Taliban.
Dr Rex Rogers, President of SAT-7 North America, said, "We're hearing from reliable sources that the Taliban demand people's phones, and if they find a downloaded Bible on your device, they will kill you immediately.
"It's incredibly dangerous right now for Afghans to have anything Christian on their phones. The Taliban have spies and informants everywhere."
The world has watched on with shock and dismay at the speed with which the Taliban retook control after US and Nato troops withdrew.
In many parts of the country, the Taliban seized control with little or no resistance.
SAT-7 PARS is broadcasting satellite Christian programmes into the country in Dari, one of Afghanistan's two official languages, and Farsi, a language understood by most Afghans.
The channel said it anticipates a 50 percent increase in calls to its counselling phone line this year as a result of the crisis.
"Because it's so dangerous to seek the company of other Christians, many Afghan believers are totally alone, with not even one other Christian with whom to talk," Rogers said.
"Our local director told me: 'Most dare not attend a house church. They're alone, fearful, and looking to us. We're their last resort.'"