At least four victims were killed Friday when a stolen truck drove into a large department store in the Swedish capital city.
Prime Minister Stefan Lofven confirmed the death toll during a late night news conference in which he said at least 15 other victims were injured in the attack.
“If it’s a terrorist act, the aim is to undermine democracy, but such acts will never succeed in Sweden,” Lofven said. “Our message is clear: You will never ever win.”
Lofven said earlier in the day that "all indications are that it was a terrorist attack”.
According to Jan Evensson, the chief of regional police, one suspect has been arrested.
"He fits the description of the person in the photo we published,” he said referring to an image police released of a man wearing a hooded sweatshirt. “We hope it’s the same guy.”
All metro stations were closed and authorities asked the public to keep away from the city center.
The government in Ankara "strongly condemned this heinous attack”, according to a Foreign Ministry statement.
"Turkey and the Turkish people, who have been the target of several similar attacks, share the grief of Sweden and the Swedish people," the ministry said.
UN Secretary-General Antonio Guterres also denounced the apparent attack while he declared the world body stood "in solidarity with the people and government of Sweden".
In Washington, the State Department condemned what it called a terrorist attack.
"Attacks like this are intended to sow the seeds of fear, but in fact they only strengthen our shared resolve to combat terrorism around the world," an agency spokesman said in a written statement.
The incident Friday follows a number of similar occurrences across Europe in which vehicles have been used as weapons and were driven into crowds of pedestrians.
More than 80 victims were killed in France after a terrorist drove a truck into crowds that were celebrating Bastille Day in Nice last July.
More recently, 12 people lost their lives in Berlin when a truck rammed shoppers at a Christmas market in the German capital.
And five people died in a terror attack outside the U.K. parliament in London a little more than two weeks ago.
The alleged perpetrator used a car to ram pedestrians crossing the Westminster Bridge.