The Confederation of Africa Football is demanding an improvement in security at the Nelson Mandela Bay Stadium, venue for Ghana's group matches at the 2013 Africa Cup of Nations.Following a pitch invasion in separate incidents by two fans during the Black Stars' opening Group B match against DR Congo, which finished 2-2 on Sunday, Caf has written to the LOC to ensure pitch security in Port Elizabeth.The Leopards have also been warned about the conduct of their fans."The Board decided to address a warning letter to the LOC advising them that they need to reinforce the Security in Port Elizabeth," a Caf Disciplinary Board decision stated."The Board also decided to address a warning letter to RD Congo as the visiting team is held responsible for the behaviour of their supporters (Article 83.3 of CAF Disciplinary Code)."A Congolese fan in the 55th minute, managed to enter the field of play and the same incident was repeated at the 65th minute when another fan entered and ran in the field of play.