CHAD and the Central African Republic (CAR) has called on the United Nations and African Union to investigate an incident at a border post in which at least six Chadian soldiers were killed by Central African troops, a joint statement said Tuesday. The incident threatens to escalate tensions between the two countries since Chad participated in African efforts to stabilise CAR in 2013, which has been wracked by rebel insurgencies ever since. "The two parties have recognised the gravity of the situation and stress the urgency of clarifying the circumstances in which this attack was carried out," the countries' foreign…