Former Thai Rak Thai Party members are under investigation and will be prosecuted if found to have financially supported an anti-government rally on Friday, junta chief General Sonthi Boonyaratglin said yesterday.

Council for National Security (CNS) chief Sonthi has a list of former Thai Rak Thai members believed to be behind the Sanam Luang rally organised by PTV.

First Army Region commander Lt-General Prayuth Chanocha suspected an "old political power group" financially supported the rally. Investigators are following the money trail.

"We believe they are behind the rally. Otherwise, the number of people attending would not have been so great. If investigations find a link, we will prosecute them under Council for National Security laws,'' he said.

 He said the government had been moderate with protesters but former power cliques exploited this leniency to create political turmoil. "From now on, we have to strictly enforce the law and urge people not to be used as political tools,'' Prayuth said.

A meeting today will consider action against anti-government groups that physically assaulted municipal police on Saturday. "We cannot allow them to hurt officials and escape the law,'' he said.

Prayuth said the CNS was investigating other offences including defamation charges. He referred to an attack against Privy Council President General Prem Tinsulanonda.

PTV chairman Veera Musigapong said another rally would proceed at Sanam Luang on Friday. If it did not receive Bangkok Metropolitan Administration approval, it would gather outside the city hall in protest.

He warned Bangkok Governor Apirak Kosayodhin not to discriminate against his group. He said the People's Alliance for Democracy had been permitted use of Sanam Luang in the past.

PTV director Nattawut Saikua said the station would organise provincial rallies soon to gauge opinion there.

Nattawut admitted PTV rallies were not part of its media role. "We wanted to carry a media role but we are not allowed to. So we have to seek justice by organising political rallies,'' he said.

Thai Rak Thai caretaker leader Chaturon Chaisang denied the party was behind the Friday protest. Those who spoke were no longer members, he said.

He said former party members now associated with PTV "want to see Thai people exercise their rights to express political views".