RIO DE JANEIRO — The story that Ryan Lochte told four days ago was frightening and detailed, the Olympic gold medalist recounting a late-night robbery and a pistol pressed against his head.

But on Thursday, Brazilian authorities presented evidence they say contradicts that account and could turn what at first had been a deeply embarrassing incident for the Summer Games' host country into a different kind of international incident.

The head of Rio de Janeiro's civil police, Fernando Veloso, said the version of the events told by Lochte and three U.S. swimming teammates was fabricated. The athletes, he said, damaged a gas station bathroom early Sunday morning and were involved in a confrontation with armed security guards before paying about $50 to resolve the matter.

“We can confirm that there was no robbery as they described, and they were not victims as they presented themselves,” Veloso told a packed news conference, alleging the athletes had given “a fantastical version of events.”

An early sign that the Americans' story had raised suspicions came late Wednesday, when authorities pulled two of the swimmers off a plane preparing to depart for the U.S. Gunnar Bentz and Jack Conger, who lives in Rockville, gave police accounts that significantly differed from Lochte's earlier statements, police said.

Contrary to reports, Veloso said none of the swimmers have been indicted.

“Indictment is a formal process that happens at the end of an investigation and hasn't taken place, at least not yet,” he said. “But there is very strong evidence that at least one of the swimmers, Ryan Lochte, made a false police report.”

Brazilian authorities said they were in contact with the FBI to determine if Lochte, who returned to his North Carolina home Monday, might be compelled to give a statement in the U.S. The other three remained in Brazil on Thursday.

Scott Blackmun, chief executive of the USOC, issued an apology shortly before midnight on Thursday.

“On behalf of the United States Olympic Committee, we apologize to our hosts in Rio and the people of Brazil for this distracting ordeal in the midst of what should rightly be a celebration of excellence,” Blackmun said.

Blackmun called the actions of the swimmers unacceptable and said the USOC will review their actions and any possible consequences when they return to the U.S. after the Games.

Earlier this week, Lochte told NBC News that he and his teammates had been celebrating at the France House for much of the night and were taking a cab back to the Olympic village when they were pulled over by armed men posing as police.

Relying on security footage and witness accounts, authorities presented a different version of events. Video from the gas station shows the four swimmers arriving after 6 a.m. Sunday and rushing into the building. They allegedly broke a door and ripped a soap dispenser from the wall.

The athletes tried to get into the wrong taxi before finding the correct one nearby. At that point, an employee of the station approached them, and they exited the car and followed him off camera.

Police said the other swimmers told them Lochte — who was the subject of a 2013 reality television series on E! called “What Would Ryan Lochte Do?” — was the most “upset” and in the most “altered” state.

At some point a gas station security guard drew his weapon to stop the swimmers from fleeing, police said. In the video, one of the four can be seen briefly raising his hands.

“We have no evidence to believe that there was any excess use of the weapon,” Veloso said, adding that the guard was an employee of the Brazilian government and was authorized to be armed.

Footage from another camera next showed the swimmers in a different area of the gas station. One had fallen onto his back and was helped up by a teammate. The four sat on a curb and could be seen in conversation with a person out of view.

The swimmers eventually stood up and left after paying for the damage.

The incident has captivated and angered residents of this oceanside metropolis.

“They owe an apology, not only to the police, but all of Brazil,” said Maria Jose Rocha, an 87-year-old retired lawyer who lives near the police station where Bentz and Conger gave their statements Thursday. “They disrespected us and underestimated our justice system.”

During a daily news briefing at Olympic Park, Rio 2016 spokesman Mario Andrada — who apologized to the swimmers before more was known about the case — took a moderate stance.

“Let's give these kids a break,” he said. “Sometimes you take actions you later regret. They are magnificent athletes. … They had fun. They made a mistake. It's part of life. Life goes on.”