Swedish police have confirmed they discovered a suspect device inside the lorry which was driven into a Stockholm department store on Friday.

The "technical device" was found in the driver's seat of the vehicle, National Police Commissioner Dan Eliasson said.

At this stage, he said it was impossible to know what it was - only that "it should not be there".

Mr Eliasson also said the suspect in custody was from Uzbekistan, 39, and known to security services.

However, he had only been seen as a "marginal character", the commissioner added.

The man remains their principal suspect in the attack, which saw a hijacked lorry driven into the front of Ahlens department store on Drottninggatan (Queen Street), one of the city's main pedestrian thoroughfares.

Eyewitnesses described horrifying scenes outside the store, as bodies and injured people lay on the ground.

Four people were killed - 10 remain in hospital, including a child. Two are in intensive care.

Swedish Prime Minister Stefan Lofven has called it a terrorist attack, with borders tightened at his request.