Eleven people were killed in a shooting at the Risbergska School in Örebro, some 125 miles west of Stockholm, on Tuesday.Police said the gunman was believed to be among those killed and a search for other possible victims was continuing at the school.

Swedish police are investigating for a motive after a school shooting in the city of Örebro that has killed at least 10 people. NBC News’ Matt Bradley reports on what is known about the 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.