Swedish police said on Saturday (8 April) that the man in custody in connection with the beer truck attack in capital Stockholm that left four dead and nearly 15 injured is the suspected driver of the vehicle.

"The person in question has been arrested as the culprit ... in this case the driver," police spokesman Lars Bystrom told Reuters. There could be other people associated with the arrested man, "but we do not know that at the current time", he added.

Police have also arrested another man in connection with the Friday (7 April) afternoon incident, according to Swedish public broadcaster SVT.

Police sources were quoted in local media reports as saying that the second man was arrested in Hjulsta in the north-west of Stockholm. He is believed to have connections with the main suspect in police custody. However, the police made no comments about further arrests.

The first man was arrested on Friday evening in Marsta, 40km north of Stockholm, after police released a grainy CCTV image of a suspect wearing a grey hood. He reportedly confessed to ramming the truck into the front of Ahlens department store on Drottninggatan (Queen Street).

Meanwhile, the country has tightened its borders following the incident, which Prime Minister Stefan Lofven termed as a "terrorist attack". Neighbouring nations Norway and Denmark have also tightened their security following the incident.

Sweden truck attack
Tow trucks pull away the beer truck that crashed into the department store Ahlens after ploughing down Drottninggatan Street in central Stockholm, Sweden Maja Suslin/TT News Agency/via Reuters

"We have investigated several people this evening, who we found interesting in one way or another, and recently we arrested someone we are very interested in," the BBC quoted police investigator Jan Evensson as saying about the Marsta arrest. The man was reportedly being held on suspicion of committing a terror offence and has been sent to a prolonged detention.

The attack area was under lockdown and nearby train stations were closed. Authorities had made arrangements in some schools and other public areas for people unable to return home due to the lockdown. Residents in the area also offered shelter to affected commuters.

Sweden attack suspect
A CCTV image released by police of the suspect in the 7 April beer truck attack in Swedish capital Stockholm Reuters/Police/Handout/TT News Agency

"We were standing by the traffic lights at Drottninggatan and then we heard some screaming and saw a truck coming," a witness, who saw the incident from his car, told Reuters.

"Then it drove into a pillar at Ahlens City, where the hood started burning. When it stopped we saw a man lying under the tyre. It was terrible to see."

The beer company that owned the truck said it was hijacked while it was making delivery earlier in the day. The delivery driver who tried to stop the attacker from stealing the truck was one of the injured victims, Reuters reported, citing Sweden's National news agency TT.

No group has so far claimed responsibility for the attack. Terror group Isis had claimed responsibility for a similar incident that took place in Nice, France in July 2016, when an attacker drove a truck into a crowd celebrating Bastille Day and killed more than 80 people. The Islamist militant group also claimed responsibility for another truck attack that took place in December 2016 at a Christmas market in Berlin in Germany.