A member of the British Olympic team has been held up at gunpoint during a night out in Rio de Janeiro, according to a report in the Guardian.
British Olympic authorities later advised athletes against going into the city, it said.
"Do not go out of the village wearing TeamGB kit or carry anything of value unless absolutely unavoidable – this makes you too big a target for theft/crime," they told athletes in the email according to the report.
"You MUST inform a member of team management if you are leaving the village and planning on staying out overnight – please do this BEFORE you leave."
The incident, which the report said had occurred early on Tuesday, has stoked concerns about the safety of competitors and visitors to Rio for South America's first Games, which conclude on Aug. 21.
"Rio is NOT a safe environment, and the level of crime has spiked in the last few days," the letter said.
"Think very carefully about whether it is worth the risk of leaving the village to celebrate after you have finished competing – BOA/UKA staff cannot guarantee your safety when away from the village/British School/British House.
"Our strong advice is that it is simply not worth the risk given the current climate in Rio."
The report comes after U.S. gold medalist Ryan Lochte and three team mates said they were robbed by armed men carrying police badges while traveling to the Athletes' Village in a taxi in the early hours of the morning after a party.