Tennis star Serena Williams has spoken out about police violence in the United States by insisting that she "won't be silent".
In a Facebook post, the 22-time Grand Slam champion admitted to feeling anxious when she eyed a policeman while being driven to a meeting by her 18-year-old nephew.
The former world number one appeared to refer to the shooting of Philando Castile, whose girlfriend live-streamed an incident with police after her partner was repeatedly shot by a white officer during a routine traffic stop in Minnesota in July.
In the post, Williams wrote: "In the distance I saw cop on the side of the road. I quickly checked to see if he was obliging by the speed limit. Than I remembered that horrible video of the woman in the car when a cop shot her boyfriend. All of this went through my mind in a matter of seconds. I even regretted not driving myself. I would never forgive myself if something happened to my nephew. He's so innocent. So were all 'the others'.
"I am a total believer that not 'everyone' is bad It is just the ones that are ignorant, afraid, uneducated, and insensitive that is affecting millions and millions of lives. Why did I have to think about this in 2016? Have we not gone through enough, opened so many doors, impacted billions of lives? But I realized we must stride on. For it's not how far we have come but how much further still we have to go.
"I than wondered than have I spoken up? I had to take a look at me. What about my nephews? What if I have a son and what about my daughters? As Dr. Martin Luther King said: 'There comes a time when silence is betrayal'. I won't be silent."
Williams is the latest American sports star to speak out about the police brutality. San Francisco 49ers quarterback Colin Kaepernick held a protest by refusing to stand for the national anthem.