One leukemia patient died and two others remain in critical condition after undergoing chemotherapy injections, a children's hospital near Tokyo said Wednesday, Kyodo reported.

Saitama Prefectural Children's Medical Center in Saitama reported the cases to police on Tuesday after finding in the patients' spinal fluid a cancer drug that should not have been used in bone marrow cavity injections, it said.

The drug is suspected of causing serious harm to the patients, all three males under age 20, including one younger than 10.

After receiving the injections between January and October of last year, one patient died this February, while the two others, including the youngest, remain in critical condition and unconscious, according to the hospital.

The drug, Vincristine, is used in intravenous injections but not marrow cavity injections, because of the known risk of neurological complications, the hospital said.

The hospital has not ruled out the possibility of the cases involving criminal activity. It said the drug had been kept in a locked room.