Hundreds of Christians were brutally slaughtered with axes and knives by a Muslim Nigerian mob on Sunday.

The Muslims attacked three small Christian villages in central Nigeria in an early-morning raid. They blocked off all exits, shot in the air, and then set upon the Christian residents of all ages as they tried to escape with axes, machetes and gunfire.

Reports of the number of dead range from nearly 400 to more than 500. Two months ago, violence between the sides claimed more than 300 people when rival youth gangs burned mosques, churches and businesses.

Nigeria, Africa’s most populous nation with over 150 million people, is about equally split between the mostly-Muslim north and the chiefly-Christian south. The center, however, is largely mixed, and native Christians vie with relatively-recent Muslim immigrant arrivals for control of fertile agricultural areas.

UN Secretary-General Ban Ki-Moon expressed sorrow Monday night at the slaughter. In a fairly restrained response, he told reporters that he is “very disturbed” at the situation, and “call[ed] upon all sides to act with maximum restraint.”