Two windows were shattered Tuesday when an Olympic bus carrying journalists was hit by an unknown projectile. There were no serious injuries.
"We don't know yet if the bus was shot, or it was a stone," organizing committee spokesman Mario Andrada told The Associated Press.
Andrada said three of the 12 journalists on the bus suffered minor injuries. Two windows were shattered, with tiny chards of glass remaining in place.
"There was kind of a popping noise and something hit two windows on the side of the bus and left two hole marks, which looked like bullet holes," David Davies, a photographer for the British-based news agency Press Association, told the AP.
He said occupants hit the floor, unsure what was happening. Davies said the bus eventually picked up a police escort.
The bus was traveling from the northern venue cluster of Deodoro to the main Olympic Park in the suburb of Barra da Tijuca.
The incident raises more concerns about security at the Rio de Janeiro Games.
Rio is deploying about 85,000 soldiers and police to secure the games, twice as many as London did four years ago.
On Saturday, a stray bullet flew through the roof of a media tent at the Olympic Equestrian Center. Officials said it had been fired from a hillside favela, but said the games had not been targeted. Organizers said the intended target was probably a security camera on a blimp.