Pedestrians flee in terror after truck ploughs into crowd in Stockholm Johnny Chadda/ Twitter

Seven people are being held by police in Sweden following a truck attack that left four people dead and another 15 injured.

A hijacked beer delivery lorry ploughed into pedestrians in Stockholm on Friday (7 April), after driving through a pedestrianised area before bursting into flames. A "suspect device" was found inside the truck.

Police have arrested a 39-year-old Uzbek man who was known to the Swedish security services, but had no known links to extremist groups. Raids were made by police at a number of properties over the weekend.

"Seven people have been brought in for questioning as a result of these events," Jonas Hysing, national head of police operations, told public broadcaster SVT. No further information was provided about the raids but Hysing said "the evidence looks very strong" that the Uzbek man was the driver of the truck, which had been hijacked, Reuters reported.

The attack came just weeks after Khalid Masood rammed a rental car through pedestrians on Westminster Bridge, London, killing four of them, then stabbed a policeman to death. In December, a similar attack on a Christmas market in Berlin by Anis Amri killed 12 people.

Prior to Friday's attack, Sweden had escaped much of the violence which has afflicted other European capitals. The country has a long record of liberalism and has been historically welcoming to migrants and refugees.

But the attack is likely to further contribute to a backlash by some Swedish citizens to their government's liberal policies. Public sentiment against migrants began to emerge after the refugee crisis in 2015, when 160,000 people applied for asylum.

Vehicular attacks by so-called "lone wolf" attackers have become a favoured tactic of extremists linked to groups such as Isis to attack so-called soft targets in the West. One of the worst attacks occurred in Nice last July, when a Tunisian man, Mohamed Lahouaiej-Bouhlel, drove a 19-tonne lorry through crowds celebrating Bastille Day in Nice, southern France.