Christians are being called upon to pray after dozens were killed in a terrorist attack at Kabul airport on Thursday.

Twin blasts hit the Abbey Gate and Baron Hotel, where the US and British forces have been stationed to help process thousands of Afghans and others fleeing the country.

The victims of the attack include 12 US troops, and Afghan nationals, including children.

ISIS has claimed responsibility.

Matias Perttula, Director of Advocacy at International Christian Concern (ICC), said he was "extremely concerned" about the deteriorating situation.

"Our thoughts and prayers are with the victims and their families of this awful attack," he said.

Harvest megachurch pastor Greg Laurie said he was "praying for Afghans in harm's way", and that he was hoping for a "swift and strategic response" from the US government.

The attack has heightened concerns for the fate of Afghan Christians, with ICC saying it confirms the "imminent threat" to them from Islamist extremists.

"The bombings today show the brutality of extremist groups which have no mercy on Afghans, Christians, and others," said ICC president Jeff King.

"The chaos in Afghanistan and at the airport caused by the Taliban and allegedly now ISIS has gone from bad to worse.

"We have been working behind the scenes for months to help Afghan Christians and will continue to do so despite any obstacle or threat. We ask everyone to continue to pray for Afghan Christians and those helping them."

ICC estimates that Christians in Afghanistan number around 10,000 to 12,000, most of them converts from Islam which makes them apostates in the eyes of the Taliban and subject to the deadliest penalties under Sharia law.

Perttula added, "The situation is a clear indicator of instability and continues to raise our concerns for the Christian community in the country and how the Taliban and other radicals will target them.

"The U.S. and its allies must look out for the at-risk communities — especially the Christians."

Gen Kenneth McKenzie of US Central Command has said the US will continue its evacuation mission in spite of the attack.

There are an estimated 1,000 US citizens believed to still be in Afghanistan.