South Africa's top prosecutor, Bulelani Ngcuka, has asked to resign after his corruption allegations against powerful Deputy President Jacob Zuma sparked a damaging political row within the ruling African National Congress. Ngcuka heads South Africa's Scorpions Unit, which last year investigated Zuma on suspicion of soliciting bribes from a French firm in exchange for contracts in a multi-billion dollar government arms deal. Zuma has denied any wrong-doing and will not be standing trial. In October, Zuma's financial advisor, Schabir Shaik, is to face trial on similar charges.