Canon Andrew White, the vicar of the only Anglican church in Iraq, has warned Christians in the country that the end of the religion in the country appears "very near".
Christians in Iraq must convert, pay a tax or be killed, members of the Iraq State of Iraq and the Levant (Isis) have said.
The majority of Christian people in the northern Iraqi city of Mosul fled when the announcement was made by the militant group last week. But Canon White has said they are trapped in the desert or on the streets with nowhere to go, and appealed for more help to counter the threat from Islamist militants.
"Things are so desperate, our people are disappearing," he told BBC Radio 4's Today programme. "We have had people massacred, their heads chopped off.
"Are we seeing the end of Christianity? We are committed come what may, we will keep going to the end, but it looks as though the end could be very near."
The vicar is in London this weekend to speak about the crisis and raise awareness of the need to provide more help to the persecuted minority.
"The Christians are in grave danger. There are literally Christians living in the desert and on the street. They have nowhere to go," he said.
As many as one million Christians had been living in Iraq prior to the US-led invasion in 2003; the majority in areas like Mosul where the communities date back to the first centuries of Christianity.
There are now thought to be fewer than half that number.