The Department of National Parks, Wildlife and Plant Conservation yesterday banned its officials from involvement in politics and threatened maximum penalties for offenders.

The ban not only prohibits department officials in executive positions from political activities but also requires them to get prior approval from the department for travel to areas outside their jurisdiction while martial law is in force.

Political commentators viewed the ban as a move against forest rangers suspected of engaging in subversive activities against the interim government.

Before the September 19 coup, forest rangers were mobilised by Yongyuth Tiyapairat, former Natural Resources and Environment minister, to counter street protests against ousted premier Thaksin Shinawatra.

The Cabinet on Tuesday moved the department's director-general, Damrong Pidet, to an advisory post in the PM's Office. Damrong was seen as a henchman of the deposed government.

Damrong's successor Somchai Phiensathaporn vowed to enforce the ban to the fullest extent. "Department officials must reform or else face the consequences," he said.

A department source said the ban was deemed necessary to free the department of politics after Damrong allowed his office to become partisan.

Earlier this week, the Seventh Infantry Regiment of the Third Army Region organised a meeting with forest rangers from Chiang Mai, Mae Hong Son and Lamphun to remind them to stick to their conservation duties.

Yesterday, the Third Army Region said in a press release that it had received more than 10 tip-offs per day about subversive activities in Chiang Mai, Chiang Rai, Kamphaeng Phet, Lampang and Phrae provinces.

The activities included the distribution of unsigned leaflets attacking the military coup.

Northern residents are encouraged to report suspicious activities or file grievances to PO Boxes 155 and 199, the press release said.

Thai Rak Thai Party acting leader Chaturon Chaisang said the authorities should not try to insinuate links between his party and the "political undercurrent" - the term used by the coup-makers to describe activities against the current administration.

"The airing of opinions should not be used as a pretext to curb basic rights," he said, reminding the authorities to clearly distinguish between legitimate views and those designed to sow social division.

Chaturon said his party had used its website to solicit views and information deemed necessary to monitor the performance of the interim government.

Sarit Ungapinant, former Chiang Rai MP and an aide to Yongyuth, denied Thai Rak Thai involvement in the "political undercurrent".