On April 1 1989, the start of the implementation of Resolution 435, clashes between Swapo guerillas and South African security forces broke out in northern Namibia . For nine days the most intense fighting in the history of the border war raged along the 300 km frontier . According to official figures, 279 Swapo combatants and 23 security force members were killed . On April 10 1989, South Africa, Angola and Cuba signed the Mount Etjo Declaration to re-establish the ceasefire and facilitate the guerillas' withdrawal to Angola through Untag assembly points.