|The suspect was shot in the leg by police and arrested|
An attacker killed two people and wounded eight in the city of Turku on Friday before police shot him in the leg and arrested him.
Police have revealed that both of the dead were Finnish. Among the injured were two Swedes and one Italian.
"The act had been investigated as murder, but during the night we received additional information which indicates that the criminal offences are now terrorist killings," police said in a statement.
"The suspect's identity is known to the police. He is an 18-year-old Moroccan citizen," it said.
Finnish police also arrested five people in a Turku apartment overnight in connection with the stabbings.
Emergency service workers at the scene of the stabbings in Finland
"There was a raid and we have now six suspects in custody, the main suspect and five others," Detective Superintendent Markus Laine of the National Bureau of Investigation told AFP.
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|Emergency service workers at the scene of the stabbings in Finland|
"We will interrogate them, after that we can tell you more. But they had been in contact with the main suspect," Mr Laine said.
The main suspect is being treated in hospital in intensive care for a gunshot wound to the thigh.
Media reports in Finland said police believed the suspect had picked his victims at random, but Mr Laine could not confirm that.
Police have said it was likely the suspect acted alone, but added they were looking for "other possible perpetrators".
Central Turku was quickly cordoned off after the attack, which occurred just after 4pm (1300 GMT).
The attack in Finland came a day after two terror-related attacks in Spain, one in Barcelona and one in Cambrils.
Four men, aged 21, 27, 28 and 34, have been arrested in connection with those attacks and remain in custody.
Three are Moroccan and one is Spanish.
Police are continuing a manhunt for Younes Abouyaaqoub, a 22-year-old Moroccan suspected of driving a van at crowds in Barcelona.