Some 40 African leaders joined French President Francois Hollande in observing a minute's silence Friday in memory of Nelson Mandela at a major summit in Paris focused on security on the continent. Hollande opened the summit with a tribute to Mandela, who died Thursday aged 95, followed by South African Foreign Minister Maite Nkoana-Mashabane who urged leaders to continue Mandela's work for peace and security on the continent.