Updated 15:02

Swedish police have confirmed that a “suspicious device” has been found in the hijacked truck used to kill four people and wound 15 others in Stockholm.

A man has been arrested on suspicion of a "terrorist crime" following the attack in Sweden's capital city.

Swedish police say the man is suspected of being the driver of the hijacked beer truck that was driven into pedestrians and rammed into a department store in the city.

Local officials say eight adults and one child remain in hospital.

Police released a photo of the suspect in the hours after Friday's attack and on Saturday they confirmed a 39-year-old man from Uzbekistan who "matches the description" had been detained.

It has emerged today that the man was known to security services with the head of the Swedish security agency, Anders Thornberg, saying the suspect "has appeared in our intelligence gathering in the past."

Swedish police chief Dan Eliasson described the detained man as a "marginal character" and confirmed officers found a suspect device in the truck.

Reports in Sweden said the device was a homemade bomb and police sources told SVT the attacker "burned" himself while trying and failing to detonate the homemade device in the Swedish capital.

Mr Eliasson said: "A technical examination is ongoing, we can't go into what it is right now... whether it's a bomb or a flammable device.

"Nothing points to (us having) the wrong person. On the contrary, suspicions have strengthened as the investigation has progressed.

"We still cannot rule out that more people are involved."

Mr Eliasson added that there were "clear similarities" to the Westminster terror attack last month.

The suspect was reportedly detained after police were notified of a man who was confused and acting strangely.

He was arrested in the suburb of Marsta, not far from the capital's Arlanda airport.

Security at borders has been heightened with a greater police presence patrolling the streets.

Terrorists can never defeat Sweden

Speaking of the attack, Sweden's Prime Minister Stefan Lofven said: "These kinds of actions will never succeed.”

“We know that our enemies are these atrocious murderers and not each other,” he said. "Our message will always be clear: you will not defeat us, you will not govern our lives, you will never, ever win."

Security at Swedish borders has been tightened and flags are to be flown at half mast in a mark of respect to victims.

Sweden's King and Queen have cut short a royal visit to Brazil and are expected to return home later on Saturday.

The brewery which owned the truck said a masked hijacker had stolen the vehicle as it made a beer delivery at a tapas restaurant. A spokesman added that the delivery driver was unharmed.

The attacker drove down Drottninggatan - known in English as Queen Street - where pedestrians doing their shopping were sent running for their lives.

Glen Foran, an Australian tourist, said: "I turned around and saw a big truck coming towards me. It swerved from side to side. It didn't look out of control, it was trying to hit people."

The truck eventually crashed into the pillar of the Ahlens department store, where the bonnet started burning.

Late into the night, forensic police were collecting evidence from the stolen vehicle, which remains at the crash site.

Officers have said there was no indication an attack was imminent and no group has claimed responsibility for the attack