Latest: Police find 'A homemade bomb' in Stockholm attack truck

Latest: A homemade bomb has been found in the hijacked truck used to kill four people and wound 15 others in Stockholm, according to local media reports.

Update - 1.15pm: A homemade bomb has been found in the hijacked truck used to kill four people and wound 15 others in Stockholm, according to local media reports.

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

Swedish police say the man is suspected of being the driver of the lorry that killed four people in Stockholm.

Fifteen others were left injured after a hijacked beer truck was driven into pedestrians and rammed into a department store in the city.

Police sources told SVT the attacker "burned" himself while trying and failing to detonate the homemade device in the Swedish capital.

The head of the country's security agency, Anders Thornberg, would not confirm the report.

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

Update - 9.45am: A man arrested in Sweden after a suspected terror attack which saw four people killed when a lorry drove into pedestrians is likely to be the driver, police said.

Police spokesman Lars Bystrom said the man is "likely" to have been the driver, but would not comment on reports in the Swedish media that he is a 39-year-old from Uzbekistan.

Mr Bystrom said only one person had been arrested in the case.

Deputy chief prosecutor Hans Ihrman approved the questioning over terror offences in the early hours of Saturday.

Earlier: Police are questioning a man on suspicion of "terrorist crimes through murder" after four were killed when a lorry mowed down pedestrians in the heart of Stockholm.

Children were among the 15 injured, emergency services said, when the suspected hijacker brought carnage to a busy shopping district in the Swedish capital.

Sweden's prime minister Stefan Lofven said "everything indicates that this is a terrorist attack" and later vowed he would not give in to attempts to destroy democracy.

Deputy chief prosecutor Hans Ihrman approved the questioning over terror offences in the early hours of Saturday.

The prime minister said: "If it is a terrorist attack, and regardless of whether it was carried out by an organisation or a lone perpetrator, the aim of terrorism is to undermine democracy, to sow discord between people so that more people will begin to hate and distrust one another.

"But those kinds of acts will never succeed in Sweden. We know that our enemy is this kind of vile murderer - not one another. We will use all of Sweden's strength to track you down.

"Our message will always be clear: you cannot suppress us, you cannot control our lives, you will never win."

Nine of those injured were left in a serious condition and reports suggested a pram was caught in the path of destruction at around 3pm on Friday.

A nationwide manhunt was launched and police arrested the man in the Stockholm area.

Detectives said he appeared to match the description of a previously-publicised image of a man they wished to speak to.

Sweden's national police force said the driver had not been detained, instead saying that the man in custody was "connected to" the incident.

Prosecutor Mr Ihrman called for him to be held over "terrorist crimes through murder" after police said he was under prolonged questioning.

Stockholm police would not comment on reports that a second man had been arrested in the northern suburb of Hjulsta but said others were still being sought.

The latest outrage inflicted on the continent came just two weeks after similar tactics were used to attack London when Muslim convert Khalid Masood drove into crowds on Westminster Bridge.

The bloodshed also bore hallmarks to attacks seen in Nice and Berlin last year.

Swedish border controls were reinforced following the attack and investigators remained at the scene after the lorry was removed.

Condemnation poured in as news of the attack broke, including statements from German chancellor Angela Merkel and Foreign Secretary Boris Johnson, who said he was "deeply concerned".

EU Commission president Jean-Claude Juncker said: "An attack on any of our member states is an attack on us all."

The Aftonbladet newspaper reported that the truck had been hijacked from Swedish beer maker Spendrups earlier on Friday.

Witness Jan Granroth told the paper that "we stood inside a shoe store and heard something ... and then people started to scream".

Mikael Anttila, a 49-year-old portfolio manager at bank SEB, told the Press Association he saw several hundred people gathered on the street close to the shop before they all started running "suddenly ... like ants".

"Then a lot of police started coming. Heavy weapons, civilian police, etc," he said.