About 10 people including the gunman have been killed at an adult education center in what Sweden’s prime minister called the country’s “worst mass shooting.”

Prime minister Ulf Kristersson on Tuesday said the attack was the worst mass shooting in Swedish history, calling it a “painful day”, while king Carl XVI Gustav conveyed his condolences. Police said the motive for the shooting at the Risbergska school in Örebro, some 200km (125 miles) west of Stockholm, was not immediately known.