A 15-year-old junior high school girl confessed Tuesday that she mailed bottles of disinfectant disguised as weight-loss medicine to 26 students and one teacher at her school in Tokyo's Minato Ward last month, police said.

One of the male students who received the package became seriously ill after drinking the substance Aug. 26. The girl, whose name has not been released, has told investigators that she meant it as a prank, police sources said.

She also said she had been influenced by earlier poisoning cases that took place in Wakayama and Niigata prefectures.

Officials of the school said the girl had been bullied by her classmates. The Metropolitan Police Department will soon turn her case over to prosecutors, the sources said.

According to police, the girl mailed the falsely labeled bottles to her classmates and one female teacher at her school around Aug. 24. The teacher was in charge of the girl's class when she was a second-year student at the school.

Attached to each package was a message saying, "If you drink this, you will have a slender body." The substance turned out to be cresol, used as a disinfectant.

The victim, a 14-year-old boy, was taken to the hospital Aug. 26 after he allegedly drank the substance. His throat, stomach and the mucous membranes in his mouth became inflamed, and a blister about the size of a golf ball formed in his throat. He is now back at school.

Police investigating the case had believed the poison was sent by a female student because the messages attached to the bottles were written in script that appeared to be that of a young girl.

Initially, the girl denied her involvement, but she surrendered to police Tuesday morning, accompanied by her father, police sources said.