Iraqi Christians, with Chaldeans forming the largest group, numbered an estimated 800,000 before the US-led invasion.
They are now half that size, with people leaving the country due to the poor security situation.
Elsewhere, at least four people were killed and 15 wounded when a bomb exploded on a minibus in the capital.
The blast occured during the morning rush hour, in an eastern area of Baghdad.
Meanwhile, in the southern city of Basra, residents say an airstrike killed four people and injured eight.
It comes a day after Iraq's prime minister ordered a nationwide freeze on raids against militias.