Police in Sweden have arrested two men after a lorry crashed into a Stockholm department store on Friday, killing at least four people.
The first man to be arrested is being held on suspicion of committing a terrorist crime by murder.
He was detained on Friday evening, after police released a grainy CCTV image of a person of interest, with a second arrest reportedly made later.
Swedish Prime Minister Stefan Lofven has called it a terrorist attack.
More than a dozen people were injured.
The country’s borders have been tightened at the prime minister’s request.
The lorry crashed into the front of Ahlens department store in the middle of the afternoon on Drottninggatan (Queen Street), one of the city’s major pedestrian thoroughfares.
The beer company that owns the vehicle said it was hijacked outside a nearby restaurant, where it was making a delivery.
Police shared the image of the man, dressed in a hooded jacket, early on Friday evening.
They confirmed a man resembling him was arrested in Marsta, 40km (25 miles) north of Stockholm.
“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,” said police investigator Jan Evensson, referring to the Marsta arrest.
He is being held on suspicion of committing a terrorist crime, the state prosecutor’s office said, and is in prolonged detention, according to a police website.
The second man, detained in the Hjulsta in the north-west of Stockholm, had links to the man arrested in Marsta, local media reported citing police sources.
Central Stockholm was in lockdown after the incident.
In the immediate aftermath, shoppers took refuge in nearby buildings for hours, waiting for the area to be secured.
The central station, which is near the Ahlens store, was evacuated.
The metro, central roads and various bus lines were also shut.
City authorities made several spaces, including a number of schools, available as temporary accommodation for those who could not get home because of transport disruptions.
Eyewitnesses described horrifying scenes outside the store, as bodies and injured people lay on the ground.
In a speech on Friday night, Prime Minister Lofven said Swedish values of democracy and freedom would not be “undermined by hatred”.
Timeline: Vehicle ramming attacks in Europe and the US
- 14 July 2016, Nice, France: A man drove a lorry for 2km (1.2 miles) through a large crowd gathered to watch Bastille Day fireworks in Nice. Eighty-six people were killed, and more than 300 injured.
- 28 November 2016, Ohio, United States: An 18-year-old student rammed his car into a group of pedestrians at Ohio State University and stabbed others. Eleven people were injured before he was shot and killed.
- 19 December 2016, Berlin, Germany: The attack in Berlin killed 12 people and injured 49, when a man drove a lorry through the crowded Breitscheidplatz Christmas market. So-called Islamic State said one of its “soldiers” carried out the attack.
- 22 March 2017, London, United Kingdom: Six people died and at least 50 were injured when a car mounted the pavement on London’s Westminster bridge and drove at high speed through pedestrians. The attacker then entered the parliament complex on foot and fatally stabbed a police officer, before being shot.
- 23 March 2017, Antwerp, Belgium: A man was caught by soldiers after he drove at a crowd. Knives, a non-lethal gun and a dangerous substance were found in his car – but no-one was injured. Terror charges were later dropped.