Party and ANC, little negotiation was achieved. CODESA 2 was held in May 1992, at which de Klerk insisted that post-apartheid South Africa must use a federal system with a rotating presidency to ensure the protection of ethnic minorities; Mandela opposed this, demanding a unitary system governed by majority rule. Following the Boipatong massacre of ANC activists by government-aided Inkatha militants, Mandela called off the negotiations, before attending a meeting of the Organisation of African Unity in Senegal, at which he called for a special session of the UN Security Council and proposed that a UN peacekeeping force be stationed in South Africa to prevent "state terrorism". Calling for domestic mass action, in August the ANC organised the largest-ever strike in South African history, and supporters marched on Pretoria. Following the Bisho massacre, in which 28 ANC supporters and one soldier were shot dead by the Ciskei Defence Force during a protest march, Mandela realised that mass action was leading to further violence and resumed negotiations in September. He agreed to do so on the conditions that all political prisoners be released, that Zulu traditional weapons be banned, and that Zulu hostels would be fenced off, the latter two measures intended to prevent further Inkatha attacks; de Klerk reluctantly agreed. The negotiations agreed that a multiracial general election would be held, resulting in a five-year coalition government of national unity and a constitutional assembly that gave the National Party continuing influence. The ANC also conceded to safeguarding the jobs of white civil servants; such concessions brought fierce internal criticism. The duo agreed on an interim constitution based on a liberal democratic model, guaranteeing separation of powers, creating a constitutional court, and including a US-style bill of rights; it also divided the country into nine provinces, each with its own premier and civil service, a concession between de Klerk's desire for federalism and Mandela's for unitary government. The democratic process was threatened by the Concerned South Africans Group (COSAG), an alliance of black ethnic-secessionist groups like Inkatha and far-right Afrikaner parties; in June 1993, one of the latter—the Afrikaner Weerstandsbeweging (AWB)—attacked the Kempton Park World Trade Centre. Following the murder of ANC activist Chris Hani, Mandela made a publicised speech to calm rioting, soon after appearing at a mass funeral in Soweto for Tambo, who had died of a stroke. In July 1993, both Mandela and de Klerk visited the United