As General Vega's forces advance eastwards towards Johannesburg, Vorster orders the deployment of South Africa's nuclear arsenal to save the city. A South African Mirage F1CZ drops a nuclear weapon on Vega's third tactical group, killing about three thousand Cuban and Libyan soldiers. The invasion force retaliates by bombarding SADF defenders with sarin gas at Potgietersrus; appalled by the carnage affecting innocent civilians, the ANC—which had previously embraced the Cubans as liberators—breaks off its alliance with Vega. Havana then authorises the use of human shields to discourage further South African nuclear strikes.