The blast occurred after the explosive device had beenplaced in a fire, a spokesman for the south prosecutor's office,Marko Uibu, said. "An investigation has to establish exactlywhat type of explosive device was involved," he added.
Uibu said the security police has launched an inquiry,basing the criminal proceeding on the Penal Code articledealing with causing an explosion by using an explosivedevice or explosive substance. Convictioncarries a prison sentence of up to 10 years.
The explosion in which four 15-year-old students ofTartu's Russian gymnasium were wounded occurred around 6p.m.
The Tartu University hospital to which the injuredteenagers were taken said two are in a serious condition and one in acritical condition. The fourth casualty was discharged afterbeing given treatment.