A bus carrying Rio Olympic journalists was hit by an unknown projectile, smashing two of its windows and leaving three media personnel with minor injuries on Tuesday.
The bus was returning from the Deodoro Olympic zone to the main press centre and was passing near the City of God slum district when it was hit.
"We haven't yet been able to confirm what kind of projectile hit the bus," organising committee spokesman Mario Andrada said, adding that the incident occurred in the Curicaca neighbourhood.
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.
"We were shot at. I mean we could hear the report of the gun," said Sherryl "Lee" Michaelson, a retired US air force captain who is working for a basketball publication in Rio.
"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 bulletholes," David Davies, a photographer for the British-based news agency Press Association, told the AP.
According to the organisers' statement, "the driver heard a noise from inside the bus which he thought was photography equipment falling down."
"Immediately, he looked in the rear view mirror and noticed that the passengers were lying on the ground.
"He continued to drive for a few metres until he saw a police car and stopped. At this time, he realised that two windows on the same side of the bus were broken."
The driver went on, escorted by the police car, "and the broken windows began to give way further."
The driver is to give a statement, while the bus is being examined by police.
Security forces had started "increased patrols," the statement said.
The International Olympic Committee said it would wait for a police report before commenting.
Violent street crime in Rio has left its mark on South America's first Olympic 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 bullet hit the equestrian centre, missing a New Zealand journalist by just a few feet.
That bullet was suspected to have been fired by a gang member trying to shoot down a police blimp or drone, officials said.
The same day, security forces conducted a controlled explosion near the finish line of the men's cycle road race.
Another suspect package was blown up on Tuesday near the luxury beachfront Copacabana Palace hotel.
Spectators leaving the Olympics opening ceremony at the famed Maracana Stadium on Friday night saw the body of a 22-year-old man who was shot dead by police in the street.
Police said the man had robbed several people in the area, but did not give further details.
A 51-year-old Brazilian woman was also shot dead during a robbery on Friday in the renovated "Marvelous Port" area, which is meant to be a main attraction for Olympic tourists.
This came a day after police confirmed that a man sitting in a car had killed a suspect who tried to carjack his luxury automobile.
Earlier in July, Belgian Olympic judo medallist Dirk Van Tichelt suffered a black eye in a late-night assault on Copacabana beach in Rio, the Belgian Olympic Committee confirmed.