There were mounting questions on Sunday about whether the deadly attack on a German Christmas market could have been prevented after it emerged that various authorities across the country had received warnings and tip-offs about the perpetrator.

Officials say four women and a 9-year-old boy were killed when a Saudi doctor drove into a Christmas market teeming with holiday shoppers in the German city of Magdeburg on Friday.

The authorities said they were struggling to understand the motives for the attack with a car in the eastern city of Magdeburg, in which a 9-year-old boy was among the five victims.