LONDON (AFP) - G4S, the British firm embroiled in a security fiasco at the London 2012 Olympics, said on Tuesday that its under-fire chief executive Nick Buckles will step down.

"G4S today announces that Nick Buckles will step down as CEO (chief executive) and retire from the company and as a director on 31 May 2013," the London-listed company said in a statement.

Mr Buckles had faced intense pressure to resign after his company failed to provide thousands of the guards it had pledged for the Games, forcing the government to draft in thousands of extra troops to fill the shortfall.

He will be succeeded by Mr Ashley Almanza, who will take up the role on June 1.

The Olympics security fiasco sparked heavy losses and reputational damage for the group.

G4S faced an inquiry by British lawmakers after it announced just days before the Olympics that it could not completely fulfil its £284-million (S$541.91-million) contract to provide 10,400 security staff for venues.