Party legal adviser Kamol Bandaipet asked why Natural Resources and Environment Minister Kasem Sanidwong na Ayudhaya failed to release results of a ministry investigation after the New Year as promised.

He said Kasem had backtracked, saying he did not now know when the investigation would be completed.

"We wonder if the ministry is trying to protect the prime minister,'' he said.

Kamol insisted the Nakhon Ratchasima forest where Surayud's mountain retreat was built is a reserve area where dwellings are prohibited, according to a 1964 Cabinet resolution.

He also cited a 1988 Cabinet resolution that said some areas of the forest had become degraded and required new planting to revive them.

He said a sign not far from Surayud's home declared the land belonged to the Electricity Generating Authority of Thailand by the permission of the Forestry Department.

"The AEC should investigate this. Forestry officials are normally afraid of governments installed by coups,'' he said.

Kamol said it was not true that Surayud purchased the land from a local villager. Former Channel 5 Television director Colonel Surarit Chantratip purchased it from a man who had bought it from a local villager for Bt700,000, he asserted.

Kamol claimed Surarit gave the land to Surayud's wife, Khunying Chitrawadee.

He accused Chitrawadee of falsely declaring in tax documents that she had not encroached on forest reserve or agricultural land.

He said although there was no tax on reserve land, the use of the land and electricity entitled village chiefs to levy a Bt5-per-rai land tax. Chitrawadee paid Bt105 per year as land tax on the 21-rai plot, he said.

Campaign for Popular Democracy secretary-general Suriyasai Katasila agreed the AEC should investigate the allegations.

AEC spokesman Sak Korsaengruang said the committee was not a "political tool" for any group and that the police or National Counter Corruption Commission should probe the allegations.