"At that precise moment we had drones flying over the favela and we also had a balloon flying over," Defense Minister Raul Jungmann told journalists.
"A possible hypothesis is that someone felt he was being followed, filmed, observed, and it's possible -- although nothing is certain yet -- that the shot was fired from there," he said.
Police, which fall under military control in Brazil, are engaged in often brutal operations against drug traffickers who control swaths of Rio's favelas, as poor, often largely unregulated neighborhoods are called. Shootings are an everyday occurrence.
A TVNZ report said the bullet narrowly missed a New Zealand team official who was badly shaken by the incident.
The Deodoro equestrian venue, where the first day of the dressage competition was being held yesterday, is on a military base.
