Pressure grew yesterday for caretaker Prime Minister Thaksin Shinawatra to name the alleged mastermind behind what he termed as a plot to topple him by unconstitutional means.

Thai Rak Thai Party deputy leader Sudarat Keyuraphan and former prime minister Chavalit Yongchaiyudh dismissed widespread speculation that Thaksin was referring to Privy Council president General Prem Tinsulanonda.

Sudarat said she believed the speculation was aimed at tarnishing the ruling party.

Meanwhile, security has been stepped up for the premier because of fears that certain elements angry with him might resort to violence, a security source said yesterday.

Thaksin has drawn flak rather than sympathy after revealing the alleged plot to overthrow him unconstitutionally. He made the remarks while addressing a gathering of top bureaucrats at Government House on Thursday.

He spent yesterday keeping tight-lipped on a burning question - who is the charismatic individual who wants to replace him by pushing for a royal intervention under Article 7 of the Constitution?

"I will one day sing for you guys," he said, dodging reporters pestering him with questions surrounding the mysterious man out to get his job.

Democrat Party leader Abhisit Vejjajiva said Thaksin risked driving a wedge in society if he failed to reveal the identity of his charismatic rival.

"In making such an inflammatory statement, Thaksin may aim at flaunting his power but ends up fanning the climate of distrust which is not conducive to ending the political crisis," he said.

Abhisit said Thaksin was trying to distract the public from the root cause of the political turmoil - the tampering with the system of checks and balances, and not the usurping of power from an elected government as he alleged.

Mahachon Party deputy leader Akapol Sorasuchart said Thaksin was trying to undermine his opponents by raising innuendoes.

"Thaksin says he will heed the royal advice on unity. But in practice he keeps making provocative comments to fan animosities," Akapol said.

Political scientist Sombat Thamrongthanyawong said Thaksin's statement was tantamount to a declaration of civil war with his opponents.

Thaksin's reference to the charismatic individual was understood by many people as a veiled attack on Thailand's revered institution, Sombat said, demanding a clarification before the situation spiralled out of control.

"Thaksin said he wanted to quell rumours surrounding his caretaker government. He should have realised that his ambiguous statement has triggered speculation like wildfire," he said.

Outgoing Senator Chirmsak Pinthong said Thaksin gushed out comments in a desperate attempt to fend off his opponents.

"I think Thaksin is putting on a brave face, even though he knows his end is near," Chirmsak said.

Chirmsak and 11 other outgoing senators yesterday co-signed a letter to Thaksin, calling on him to identify the charismatic individual. The letter also urged Thaksin to launch an investigation into that particular individual if the premier was certain the person was up to something undemocratic.

With regard to Thaksin's remarks that charismatic people and some organisations outside those sanctioned by the Constitution are trying to impose changes, outgoing Senator Sophon Suphapong said this was completely false.

Every citizen and organisation is under the Constitution and there are no individuals or entities that can exist outside its provisions, he said.

The government's opponents are sanctioned by the Constitution to exercise their rights to safeguard democratic rule when they have detected harmful consequences of a rogue regime, he said.

Southern Thai Studies Institute lecturer Charoon Nooyong said a majority of Songkhla residents understood that Thaksin was trying to smear the Privy Council president, who is their native son.

"Thaksin must clarify his statement before it is too late to do so," Charoon said, warning that local residents will not tolerate such remarks.

Suriyasai Katasila, spokesperson for the People's Alliance for Democracy, said although Thaksin did not name the charismatic individual, many people thought about the Privy Council president.

"Thaksin defamed the reputation of General Prem, but he thought he could get away with it by not mentioning his name. Thaksin killed two birds with one bullet - one was to convince the public that there is an unconstitutional plot to topple him, and the other was that the person he referred to was discredited," Suriyasai said.

Government critic Sondhi Limthongkul said yesterday that Thaksin's remark was aimed at pitching his supporters against his critics.

"The prime minister is causing a rift in society. He's bringing Thailand to a point where a bloodbath is unavoidable," he said.