A Japanese pop star has been left in critical condition after being stabbed by a fan just before a scheduled performance in Tokyo.

Mayu Tomita was stabbed over 20 times, sustaining injuries to her chest and neck. Reports say Tomohiro Iwazaki, an alleged fan of Tomita, attacked her after she returned a gift he had given her.

Police told KYODO, a local news source, that the incident took place in Koganei, a venue in west Tokyo on Saturday at 5pm, before the 20-year-old singer was due to perform. Iwazaki, 27, is said to have been reported by eyewitnesses on the scene, where he then confessed to the crime.

Japan Times wrote that police told them the suspect said: “I ambushed her at the station and asked her (about the gift). I lost my temper and stabbed her many times because she didn’t clearly answer.”

In messages taken from Tomita’s social media accounts, a user claimed to have sent her a watch, which was returned in April. “I will never forget that I was looked down upon by you,” it read. “It would be radical to kill just because (someone was) rejected by a girl,” read another message from March.

Asahi Shimbun, another Japanese publication, said Tomita had previously complained to police about an “obsessive” male fan, who stalked her and sent incessant messages on social media.

As of Sunday 22 May, Tomita is said to still be in critical condition.