STOCKHOLM - Swedish police have brought in seven people for questioning over an apparent terror attack in which a hijacked delivery truck mowed down pedestrians in Stockholm, killing four people, authorities said on Sunday.

A 39-year-old Uzbek man was arrested earlier as the suspected driver of the truck that rammed into crowds in the Swedish capital on Friday.

The man had been known to Swedish security services and police said he had shown an interest in extremist groups. He also had his permanent residency application rejected in June last year.

A further 15 people were injured when the beer delivery truck barreled down a busy shopping street before crashing into a department store and catching fire.

"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, after several raids on addresses around Stockholm over the weekend.

Hysing declined to give further information about the raids, but said "the evidence looks very strong" that the Uzbek man was the driver of the commandeered truck.

In neighboring Norway early on Sunday, police set off a controlled explosion of a "bomb-like device" in central Oslo and took a suspect into custody. Police across the Nordic region went on heightened alert after the Stockholm attack.

Vehicles have also been used as weapons in Nice and Berlin in the past year in attacks claimed by Islamic State.