About 10 people, including the gunman, were killed on Tuesday at an adult education center in what Sweden’s prime minister called the country’s “worst mass shooting.” But a final death toll and a conclusive number of wounded hadn’t yet been determined.

Prime Minister Ulf Kristersson gave a news conference hours after the tragedy.

“Today, we have witnessed brutal, deadly violence against completely innocent people,” Kristersson told reporters. “This is the worst mass shooting in Swedish history. Many questions remain unanswered, and I cannot provide those answers either.

“But the time will come when we will know what happened, how it could occur, and what motives may have been behind it. Let us not speculate,” he said.

The damage at the crime scene was so extensive that investigators were unable to be more definitive, said Roberto Eid Forest, head of the local police. The shooting happened on the outskirts of the city of Orebro, which is located about 200 kilometers (125 miles) west of Stockholm.

Police said that the death toll could rise. Eid Forest told reporters that the suspected gunman was among those killed. Police believe the perpetrator acted alone, and he wasn’t previously known to police, officials said.

Authorities said that there were no suspected connections to terrorism at this point, but police didn’t provide a motive.

The school, called Campus Risbergska, serves students who are over age 20, according to its website. Primary and upper secondary school courses are offered, as well as Swedish classes for immigrants, vocational training and programs for people with intellectual disabilities.

Gun violence at schools is very rare in Sweden. But there have been several incidents in recent years in which people were wounded or killed with other weapons such as knives or axes.

Police raided the suspect’s home after Tuesday’s shooting, but it wasn’t immediately clear what they found. Eid Forest said there were no warning signs before the attack. Authorities were working to identify the deceased.

Earlier, Kristersson said that it was “a very painful day for all of Sweden,” Swedish media reported.

“My thoughts are also with all those whose normal school day was exchanged for terror,” Kristersson said. “Being confined to a classroom with fear for your own life is a nightmare that no one should have to experience.”

Swedish King Carl XVI Gustaf praised police and the rescue and medical personnel who responded to the shooting, and issued words of comfort to the families of the victims.

“It is with sadness and dismay that my family and I have received the information about the terrible atrocity in Örebro,” the monarch said in a statement. “We send our condolences tonight to the families and friends of the deceased. Our thoughts at this time also go to the injured and their relatives, as well as to others affected.”

The shooting erupted after many students had gone home following a national exam. Police vehicles and ambulances, lights flashing, blanketed the parking lots and streets around the school as a helicopter buzzed overhead.

Teacher Lena Warenmark told SVT News that there were unusually few students on the campus Tuesday afternoon after the exam. She also told the broadcaster that she heard probably 10 gunshots.

Students sheltered in nearby buildings. Other parts of the school were evacuated following the shooting, which began at around 12:30 p.m. local time (1130 GMT).

Andreas Sundling, 28, was among those forced to barricade themselves inside the school.

“We heard three bangs and loud screams,” he told Expressen newspaper while sheltering in a classroom.

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Geir Moulson contributed to this report from Berlin.