RIO DE JANEIRO, Aug 7 (Reuters) - Organisers of the Rio 2016 equestrian event on Sunday demanded answers from Olympic bosses and assurances of safety after a bullet ripped through the plastic roof of their competition centre a day earlier.
"Obviously this is a worrying situation and is not an incident we can take lightly as the safety of everyone at our venue - athletes, horses, media and spectators - is of prime importance," Ingmar De Vos, president of the International Equestrian Federation (FEI), said.
The venue was not a target in any way, according to local organisers, citing the Brazilian military, the civil police and the national guard.
"These authorities are conducting a full investigation into the matter and have assured the Organising Committee that they have reinforced security around and inside the equestrian venue," De Vos said.
"The FEI is actively monitoring the situation and we have asked for confirmation about the measures that have been put in place to ensure there will not be a recurrence."
The equestrian venue is sited next to a military complex, fuelling speculation that the bullet could have come from a firing range.
However, a defence ministry spokesman said the bullet came from a neighbouring community, although it was unclear exactly where.
With high levels of violent crime in Brazil's slums, some of which are controlled by drug trafficking gangs, stray bullets are a concern for residents.
Another theory is that the bullet came from a favela dweller shooting at a police drone. Drug gangs in the favelas are fiercely protective of the privacy of their operations from police and rival gangs.
A Rio 2016 organising committee spokesman said on Sunday the investigation was still ongoing. Like an unattended backpack that anti-bomb police detonated on Friday as a precaution, the stray bullet may have been related to security measures, he said.
Saturday's bullet, bronze in colour, landed close to American photographer Rob Carr.
"We were sitting down there a little after one o'clock. Myself and my colleague were sitting about 10 feet up and you heard this cracking and rattling sound that sounded like something hitting metal and like five seconds go by and someone's like 'Oh my God there's a bullet on the floor'," he told Reuters.
"That bullet was 10 feet away from me and closer to a lot of people."
Carr said he had been listening to gunfire all Sunday morning.
Two soldiers stationed outside the centre told Reuters any sounds of shooting must have been from the shooting competition, as no military drills were being conducted on Sunday.
The Olympic shooting range is 2.6 kilometres away.
Security has become a major concern for organizers of South America's first Olympics. Brazil has deployed 85,000 police, military, and private security personnel for the Games, more than double that of London in 2012. (Additional reporting by Anthony Boadle in Brasilia; Editing by Daniel Flynn and David Evans)