Option 1 and 2 are incorrect because there`s no concrete information to indicate that South African soldiers were sent to Burundi to side with either Tutsi or Hutu tribes in any conflict. The soldiers` objective is not to take sides in any ethnic war but to restore peace.

Option 3 seems plausible but is also incorrect as it suggests the troops were sent as a part of the United Nations` special force to control ethnic groups revolting against the government. There`s no evidence to show they were part of a UN force.

The correct answer is Option 4 as it accurately suggests that South African soldiers were sent to Burundi as a protection force to help mediate an agreement between the warring groups of the civil war. This aligns with South Africa`s peacekeeping roles across the African continent. It strongly indicates that the soldiers have a non-combatant role aimed at fostering peace and reconciliation among conflicting parties.