A knife-wielding man hijacked a bus in Norway and killed three people on board, including the bus driver, police said.
The suspect, described as a man in his 50s, has been arrested.
Police spokesman Odd Arve Solvag says the fire department responded to the incident at first in the belief that it was an accident. They apprehended the man who was later arrested by police.
The motive was not immediately clear.
Mr Solvag said the suspect was not an ethnic Norwegian but could not give details on where he was from.
Oslo police was getting ready to send an anti-terror unit to the scene aboard army helicopters but called off the deployment after receiving reports that the suspect had been arrested.
"The situation was very unclear. They only told us that there was one man on the bus who had hijacked the bus and the driver was hurt. That was the first message we got here," Oslo police spokesman Andre Krakenes said.
Multiple killings are rare in Norway, though the country was shocked by its worst peacetime massacre two years ago when a right-wing extremist killed 77 people in a bomb and gun rampage.