2 August 1963
The United States (US) informed the United Nations (UN) on 7 August, 1963 that it would suspend sales of arms to South Africa. The Security Council adopted Resolution 181 calling upon all states to cease the sale and shipment of arms, ammunition and military vehicles to South Africa. The arms embargo was made mandatory on 4 November, 1977. The sanctions against South Africa were prompted by the county’s infamous Apartheid policy, which brought about race segregation.
References

United Nations, ‘Nelson Mandela Internationals Day’, [online], available at www.un.org (Accessed: 18 July 2013)|Boddy-Evans, A. ‘This Day in African History: 02 August’, from About African History, [online], available at https://africanhistory.about.com (Accessed: 18 July 2013)