Six educators were killed this week in the Central African Republic, Unicef said on Wednesday, the latest of several attacks on aid workers as that fragmented and war-torn nation slides deeper into chaos.

The attack occurred near Markounda, a small town in the northwest, near the border with Chad — a remote part of a sparsely populated country that is sometimes described as the least developed in the world. Like most of the nation, the area is beyond the control of the central government in the capital, Bangui, and power is wielded instead by an array of militias that often fight one another.

Last August, six Red Cross volunteers were killed in the southeastern part of the country, and there have been other acts of violence against aid workers since then. Days after the August attack, the United Nations warned of rapidly escalating violence and a worsening humanitarian crisis in the Central African Republic.

Even the most intrepid aid groups have reconsidered whether it is safe to work in the country. In November, Doctors Without Borders shut down a major operation after a string of attacks and threats.