The reason is that fireworks were set off inside the wedding hall as part of the celebrations. In a v ideo from BBCYou can see how what looks like large sparklers ignite the ceiling lining. Flames then fall on the guests, who then run towards the exits of the ballroom.
It does not appear that the fire was caused by Islamic terror against Christians.
It's a tragedy for the Christian minority. In 2014, the Islamic State seized land in Iraq and expelled Christians from areas where they had lived for centuries. Many Christians sought refuge in the independent province of Kurdistan or fled abroad.
Samuel Nymann Eriksen from the Danish European Mission says: "It touches me, not least because I have visited Iraq twice. I have met Christians who had to flee from Qaraqosh, which the Islamic State had taken at the time. It is in every way tragic what has happened and we must pray for the country's Christians and the authorities."
In 2003, there were an estimated 1.5 million Christians in Iraq, while today the number is below an estimated 200,000.