Police say the attacker, who was shot dead by police, is being investigated for possible far-right sympathies.

Investigator Thord Haraldsson said a racist motive was “part of the picture” but did not reveal further details.

Two others were critically injured in the attack at the school in Trollhattan on Thursday morning.

The attacker, 21, was seen posing for a photograph with students, who thought he was dressed for Halloween, before going on the rampage from classroom to classroom, sending panicked students fleeing from the school building.

A teacher and 17-year-old boy died from stab wounds, while another male student, 15, and 41-year-old teacher remain in serious condition in hospital.