Two members of popular Japanese pop group AKB48 were injured after a man attacked them with a saw.
Rina Kawaei, 19, and Anna Iriyama, 18, were meeting with fans in the northern city of Takizawa on Sunday when a man lunged forward and slashed them.
They sustained cuts on their hands and heads, reported Kyodo. A male staff member was also cut on his hand.
The group holds the Guinness record for being the world's largest pop group.
The police have arrested the 24-year-old man, identified as Satoru Umeta.
AKB48's manager was reported as saying the two girls' surgery was successful and they would be able to leave the hospital by Monday.
A Tokyo concert scheduled for Monday night and other fan events have been cancelled.
News of the attack was covered widely in national media. AKB48, which was founded in 2005, is hugely popular in Japan and other Asian countries.
AKB stands for Akihabara, the technology district of Tokyo, where the group has its own theatre. Members perform there almost every day.
The number 48 reportedly refers to the original number of members in the group, although it has since expanded.
The current line-up on the group's website, spread over four main teams and other smaller ones, lists 140 names.
Every year tens of thousands of fans vote on who gets to join the group from a pool of more than 200 candidates, in an event that is widely covered by national media.
Members have to abide by strict rules set by their management, and are not allowed to date.
The band made international headlines last year when one of its members, Minami Minegishi, shaved her head and apologised to fans in a video posted online. She had been caught spending a night with her boyfriend.
The incident sparked debate on whether pop idols in Japan have the right to lead normal lives.