RIO DE JANEIRO (AFP) - They stand discreetly in the shadows, eyes keenly on the look-out, as women's world number one tennis star Serena Williams perfects her blistering forehand at the Rio Olympics.
Their presence is low key, but the United States has a team of Diplomatic Security (DS) personnel in Brazil serving in support roles with under-the-cosh local forces.
Security has been a major talking point at the Games, which officially open on Friday (Aug 5), with athletes, officials, fans and media from numerous countries reporting they have been victims of crime.
Brazilian authorities are responsible for overall security for the Olympics, but countries and teams have added their own extra layer to ensure that some of the biggest names in sport are safe.
It is not merely the American stars such as the Williams sisters Serena and Venus where DS agents provide a reassuring presence.
The agents also liaise with Brazilian security and law-enforcement officials, as is standard for large international events like the Games in Rio, where thousands of Americans - fans, athletes, corporate sponsors and media - are in town for sometimes weeks at a time.
The US State Department's advice for Rio makes for alarming reading, warning of armed robberies and crime that "can happen at any place or time".
"While criminal activity is more frequent in certain areas, there is no area in Rio that is immune," says the State Department.
Muggings, car-jackings and shootings are all a major concern, it says, adding: "There have been reports of thieves and rapists slipping incapacitating drugs into drinks at bars, hotel rooms, and street parties."
As the United States does in many countries, American officials also worked with Brazilian authorities in the lead-up to the Olympics to provide training for local law enforcement.
At the Brazilian government's request, the DS worked together in a variety of areas, ranging from airport screening procedures to managing entry-exit at stadiums to preventing serious security incidents.