"I may need to propose this measure to prevent them from causing trouble," director-general Paisal Wichienkua said yesterday.

The department's juvenile observation and protection centres were designed and its staff trained to deal with young inmates, not those aged 18-24 who were filling up the centres, he said.

Of over 6,000 inmates in the department's system, nearly 3,000 were in that age range.

Control measures used for the young occupants would not be very efficient when applied to older convicts, who were usually blamed for instigating the violence.

The department would ask the Justice Ministry to amend laws to ensure that those over 18 when arrested were sent to prisons, not the youth rehabilitation centres.

"Convicts who are almost 18 years old and receive a long jail term should be sent to prisons," Paisal said, adding that those at the juvenile centres should not be over 20.

As an immediate measure, he ordered officials to block inmates access to news about breakouts or violence at other correction facilities. "Also, the gang leaders behind any incident should be subjected to temporary custody at prisons or military camps," he said.