Corrections Department director-general Pol Col Suchart Wong-anantachai has set up a committee to investigate the staff of the Nakhon Si Thammarat prison, reports said.

The action followed a surprise raid on the prison on Sunday by hundreds of corrections officials and police during which 284 mobile phones, including dozens of smart phones, about 1,700 methamphetamine pills, 50 grammes of ya ice, or crystal methamphetamine, and many other forbidden objects were found.

Most of these items belonged to drug convicts believed to have been continuing their illicit trade from inside the prison.

The Nakhon Si Thammarat prison chief, Narong Yongnarongdejkul, was immediately transferred to an inactive position at the Corrections Department pending investigation.

At least 10 officials of the prison were believed to be involved in the drug trade and they are also subject to further investigation.

The Corrections Depatment was reportedly considering setting up a mobile phone signal jammer at the Nakhon Si Thammarat prison to cut off the drug trade.  The prison is the largest in the South, with more than 4,000 inmates.

The department now plans to transfer some major drug convicts to Khao Bin prison in Ratchaburi province.