Officials say five people have been killed, including a 9-year-old, after a Saudi doctor drove into a Christmas market teeming with holiday shoppers in the German city of Magdeburg on Friday.

The latest deadly assault on a beloved German tradition illustrates the challenge of holiday safety. For years, Germany has been strengthening security measures around Christmas markets in reaction to an attack in 2016 in which a man killed 12 people by driving a truck into a market in central Berlin.