UPDATE 1-Security giant G4S says will avoid soccer World Cup

* CEO says concerned over organisation

* Says South Africa is most difficult market in the world

* World Cup organisers say confident of security

* G4S to focus on ports, oil and aviation sectors (adds reaction from World Cup organisers)

By John Bowker

LONDON, May 20 (Reuters) - G4S, the world's biggest security firm, will not operate at next summer's soccer World Cup in South Africa because of concerns over the tournament's organisation, the group's chief executive told Reuters.

"We are not going to be involved because we don't think the security is going to be that good -- they are not that well organised yet," Nick Buckles said in an interview.

But Danny Jordaan, chief executive of the 2010 organising committee, rejected the concerns, saying he was confident the tournament would be safe. He referred to criticism from "individual companies with vested interests."

Jordaan said his country had hosted many major international and sporting events, including the current Indian Premier League Cricket competition, which was moved to South Africa at short notice because of security concerns during India's general election.