A family court has sentenced an 11-year-old girl to a state-run juvenile correctional facility in eastern Japan for killing her classmate with a box-cutter (search), an official said Wednesday.

In a closed-door session, judges at the Nagasaki prefecture Family Court ordered the girl to undergo counseling as part of a rehabilitation program at the facility in Tochigi prefecture, just north of Tokyo, a court official said on condition of anonymity.

It was unclear how long she might have to stay. The facility for girls is the only one in Japan with lockup cells, the official said. Her case was expected to be reviewed later, based on recommendations from counselors and psychiatrists.

The sixth-grader has been in juvenile detention since early June, when she allegedly led 12-year-old Satomi Mitarai (search) to an empty classroom during their lunch hour, slit her neck and arms with a box-cutter, and left her to bleed to death.

Investigators believe the two had exchanged nasty messages over the Internet.

Under Japanese law, she cannot be tried for criminal responsibility because she is under 14. But the family court ruled on her case after she underwent psychiatric tests. The girl's name will not be released because she is a juvenile.

At a news conference following the court's ruling Wednesday, defense attorneys called the decision "appropriate."

Increased juvenile crime and violence at schools in recent years have eroded Japan's image as a safe haven, relatively free of crime.

Last July, a 12-year-old boy in Nagasaki was accused of kidnapping, molesting and killing a 4-year-old by shoving him off a roof. In 1997, a 14-year-old beheaded an 11-year-old neighbor.