Victims of ISIS' deadly attack on a bus in Egypt were asked to renounce their Christian faith and when they refused they were shot dead, a senior Coptic bishop has confirmed.

Girls as young as two were among the 29 killed as militants targeted pilgrims en route to a monastery near the town of Menya in southern Egypt.

Bishop Makarios, the top Coptic Orthodox cleric in Minya, said the assailants ordered victims off the bus and told them their lives would be spared if they converted to Islam.

'They chose death,' said Makarios, according to the Associated Press.

'We take pride to die while holding on to our faith,' he said in a television interview, the agency reported.

The bishop has been an outspoken critic of the government's handling of anti-Christian violence in Minya, where Christians account for more than 35 percent of the population, the highest anywhere in Egypt.

Bishop Angaelos, head of the UK Coptic Church and in regular contact with his counterparts in Egypt, also confirmed those killed had been asked to renounce their faith.

In an extraordinary message directly to the perpetrators on Tuesday, Angaelos said: 'You are loved. The violent and deadly crimes you perpetrate are abhorrent and detestable, but YOU are loved.

'You are loved by God, your Creator, for He created you in His Image and according to His Likeness, and placed you on this earth for much greater things, according to His plan for all humankind.

'You are loved by me and millions like me, not because of what you do, but what you are capable of as that wonderful creation of God, Who has created us with a shared humanity. You are loved by me and millions like me because I, and we, believe in transformation.'

His statement comes after Egypt responded to the attack with a wave of airstrikes against suspected militant bases where the military said the perpetrators trained. A large-scale manhunt by police and soldiers backed by helicopters is underway in the vast deserts to the west of the site of the attack, but has so far yielded no arrests.