At least 10 killed at adult education center in what officials say is Sweden's worst mass shooting

The school, called Campus Risbergska, serves students 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.

"Today, we have witnessed brutal, deadly violence against completely innocent people," Kristersson told reporters in Stockholm. "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.

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.

Justice Minister Gunnar Strömmer called the shooting "an event that shakes our entire society to its core."

While Swedes read about such violence in other places, Strömmer said that the country previously felt it wouldn't happen there. Other tragedies in Swedish schools weren't to the extent of Tuesday's attack, he said, calling it "indescribably sad" for the community.

The shooting also sent shockwaves through Europe, with officials in Brussels expressing their outrage at the carnage.

"What happened today in Örebro is truly horrifying," European Commission President Ursula von der Leyen wrote on social media. "Such violence and terror have no place in our societies — least of all in schools. In this dark hour, we stand with the people of Sweden."

The damage at the crime scene was so extensive that investigators were unable to be more definitive about the number of fatalities, said Roberto Eid Forest, head of the local police.

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.

"Of course, we all want to understand why this happened, what occurred, and what motives the perpetrator may have had," Kristersson said. "We will have to wait for those answers — in due time, the picture will become clearer."

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.

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.