Mourners are laying flowers near the scene of the deadly Christmas market attack as investigators puzzle over the motive of the suspect.

Hundreds of people in Magdeburg formed a human chain on Monday to remember the victims of the attack on a Christmas market in the city, and to stand against right-wing extremists seeking to exploit the killings.

The alleged perpetrator of the deadly car-ramming attack on a Christmas market last week in Germany had been contacted by police just weeks before the incident, authorities said on Monday, as the number of people injured climbed to 235.