JOHANNESBURG: South African police stepped in to take over security at four World Cup venues Tuesday after new strikes by stewards, including a walk-out hours before Brazil's first match of the tournament.South Africa's government said the move would not affect fans' safety but organisers were left red-faced by the failure to contain the industrial unrest.National police commissioner Bheki Cele said his officers would now be in charge of security at the stadiums in Durban, Cape Town, Port Elizabeth and Johannesburg's Ellis Park where five-times champions Brazil played North Korea.Around 1,000 police were on duty in and around the ground for one of the most eagerly awaited matches of the first round."We have activated necessary and adequate contingency plans to different stadia in the country," said Cele. "We are confident that we will not compromise the safety of the tournament or our day to day normal policing."A correspondent at Ellis Park reported several hundred staff walked out of the stadium around four hours before kick-off.