Police are searching for a man wearing a clown mask and a yellow jacket who stabbed a person in southern Sweden.
Police spokeswoman Ulla Brehm said there have been two similar incidents where people dressed like clowns stood outside schools and scared children.
“This is not a crime as such but very, very unpleasant,” she added.
Ms Brehm said the incidents are likely to have spread via social media from the United States, adding: “It is not funny when people are being scared.”
She said a 19-year-old man was stabbed late on Thursday with a knife in the shoulder in Varberg, south of Goteborg.
He sustained superficial wounds and despite searches, the attacker has not been found.
Similar incidents were reported elsewhere in Sweden, Denmark and Norway – where the Ringo toy store chain decided to stop selling clown costumes in its 114 shops.
“We have done so in the wake of the recent so-called ‘killer clowns’ episodes,” Ringo chain chief executive Gro Svendsen said.
“This is a phenomenon which we strongly oppose. Costumes and disguises should be for fun and not motivated by the desire to spread fear.”