Facebook's Safety Check feature was activated Monday in the wake of a deadly truck crash that killed at least nine people and injured dozens more at a crowded market in Berlin.
Berlin police encouraged people in the area to use the Safety Check feature to let friends and loved ones know they are safe after the truck rammed the crowded Christmas market at Breitscheidplatz, a major square in the center of the German capital.
Safety Check sends a message to Facebook users in areas of immediate danger, allowing people to notify friends and family that they are alive and well. It has been used for natural disasters like hurricanes, as well as mass shootings and terrorist attacks.
Facebook has activated the tool at least 40 times in the past two years, but it has also been criticized for failing to activate Safety Check in some parts of the world. In response, the social media giant no longer manually activates the tool, relying instead on its 1.2 billion daily visitors to help automatically launch the feature.
The US said the incident "appears to have been a terrorist attack." White House National Security Council spokesman Ned Price condemned the attack and said the US is ready to assist Germany in investigating the incident and responding to it, according to the Associated Press.