Swedish police said Sunday they were investigating the attempted murder of an 11-year-old Norwegian boy who was found hanging by the neck from a tree at camping grounds in western Sweden.

The boy survived by standing on the tips of his toes, struggling to breathe, for about 10 minutes, when he was rescued by a passerby.

"The investigation is ongoing... we do not have any suspects," Leif Hultman of the Värmland county police told AFP, adding the crime had been classified as attempted murder.

The victim, who was vacationing with his family in the area, was playing alone at the camping site's playground when he was attacked from behind at around 9:00 pm (1900 GMT) Friday.

Hultman said it was not clear if there was one or many attackers.

The attacker or attackers covered the boy's face, tied a rope around the boy's neck and hoisted him up before fastening the rope to a tree branch.

"My son is a quiet boy and has never hurt a fly," the boy's father told Norway's VG Nett news website, saying the incident could have easily been a lot worse.

The father added he suspected young people were the attackers, based on his son's description of their height.

The boy received care at a hospital and is still in Sweden, Hultman said.