Parties were held by inmates of the central Nakhon Si Thammarat prison in violation of prison regulations, made possible by corrupt guards allowing in narcotics and contraband items, deputy Corrections Department director general Kobkiat Kasiwiwat admitted yesterday.
Use of drugs is believed to have been free and rampant - information supported by video clips extracted from seized mobile handsets.
When a third round of prison searches turned up another 39 mobile phones - after more than 400 handsets had been found in two earlier searches - Kobkiat admitted to the drug parties after video clips shot by inmates had been extracted.
"There will likely be more handsets found hidden in the prison while the searches continue," he added.
Allegedly corrupt guards would be disciplined, pending an internal investigation, he added.
The new prison commander, Suraphol Kaewparadai, took over yesterday and inspected safety procedures.
New measures would require all guards and even the commander to undergo mandatory processes, including a daily body search, when they entered detention areas in the prison.
He said the latest 39 phones to be discovered were hidden in concrete walls.
Five handsets were retrieved from an inmate who was openly using one, apparently unaware that recently installed security cameras had become operational.
Citing records from October last year to March 31, Suraphol said 1,004 mobile phones and 723 SIM cards had been found in 192 prison searches.
Forty-three attempts to hurl units over the wall had been detected.
A total of 554 amphetamine tablets, 152 grams of "ice" crystals and 1.062 kg of marijuana were found.
Eleven drug dealers involved in the in-prison dealings had been identified, and six other cases were being probed, said deputy provincial police chief Pol Colonel Phoodis Norrasing.
Four cases were being processed criminally and three others had so far failed to identify wrongdoers.
Local police had received 220 complaints for further prosecution.
The officer said many of the recently found 39 units were smuggled into the prison by an inmate convicted of murder, who later resold them for a large profit.
The Interior Ministry said the number of jailed drug users seeking rehabilitation had increased by 30 per cent, after an agreement was signed between provincial and local authorities, compared to only 2 per cent earlier.
Deputy permanent secretary Pracha Terat said the ongoing crackdown on prison drug dealing depended on action by provincial authorities who initiate searches.