A journalist on board a Rio 2016 media transport bus that had two windows smashed while it was travelling from a venue to the Olympic park has said the damage was caused by gunfire.
Lee Michaelson, a reporter on women's basketball who is also a retired US Air Force captain, said she instinctively hit the floor when she heard the sound of gunfire and called on other passengers to do the same.
Police are investigating but Olympic officials have said it is not clear whether the incident was caused by bullets or stones.
Speaking to the Press Association, Ms Michaelson said: "I know what a gun sounds like. There was a very distinctive sound of the report of a gun. It was the sound before I ever saw the glass or anything.
"With my background and training, I got down on the floor as much as I could and I hollered to the others to get down.
"The others were just beginning to respond. I started yelling at them, 'Get down, get down, we are taking fire'."
The 63-year-old said a cameraman next to her who had experience reporting from the war in Iraq also thought it was gunfire.
She thinks, because of the noise and the angle of the holes in the window, the shots were fired from a handgun, not a rifle.
Ms Michaelson also described the reaction of the driver, who slowed down and pulled over to the side of the road.
"I found that absolutely shocking that there appeared to be no training. It was precisely the opposite of what he should have done which was to put the gas on and floor it until he had a secure position," she said.
She said the lights on the bus were also left on which left the 12 journalists on board "sitting there like turkeys".
Ms Michaelson said, despite being impressed by the welcoming attitude of volunteers at the Games in general, she was concerned by the response of Olympic officials to the incident.
She said no ambulance was waiting for them when they returned to the Olympic park, despite some passengers, including a Turkish volunteer and a Belarussian broadcaster, being injured and bleeding.
"Nobody from Rio 2016 came and asked about what happened," she said.
"It could have been life-threatening. It would have been nice if somebody had been there to ask."