Switzerland has refused to reopen long-running graft cases against Pakistani President Asif Ali Zardari as he enjoys immunity as head of state, Pakistan's law ministry said on Sunday. Pakistan wrote to Swiss authorities in October over the multi-million dollar allegations against Zardari, which date back to the 1990s, at the insistence of the country's Supreme Court. Zardari and his late wife, former premier Benazir Bhutto, were accused of using Swiss banks to launder $12 million in alleged kickbacks.