On Sunday Islamic State released a video seeming to show the executions of a group of believers.
Al-Azhar, a Sunni Islam organisation, denounced the killings saying they do not represent Islam.
The group said the executions were a "heinous terrorist crime committed by a terrorist group".
During the video a masked IS militant says Christians must convert to Islam, pay a special tax or be killed.
Images showed two separate groups of Christians, one being beheaded and the other shot dead.
In a statement Al-Azhar added that the actions of Islamic State and "other similar organisations do not comply by any means with any religion, human laws and customs".