Their surrender came after the People's Alliance for Democracy (PAD) threatened to organise more anti-government rallies if police did not handle the matter properly.

The two men were identified as Charan Chong-on, 43, a rubber farmer and Surat Thani native (who wore a black T-shirt during Monday's melee), and Chaiyasit Lamoh, 42, a motorcycle taxi rider from Bangkok's Lat Krabang district.

Their surrender came as the police tried hard to distance themselves from the two men, who were highly sought after by the media and general public for their heavy-handed tactics.

The two men, one dressed in black and another one in peach coloured shirt, were caught on camera by photographers punching and kicking the handful of anti-Thaksin protesters - as uniformed police officers looked on.

The attacks came as the protesters hollered "Thaksin get out" at the entrance of the Central World shopping complex. Thak-sin went there for a social function.

Pol Colonel Manit Wongsom-boon, deputy commander of the Metropolitan Police Division 6, maintained that the two men were not police officers. "They are definitely not policemen because we would recognise them if they were," Manit said.

Chaiyasit said he and Charan, who he has known for more than 10 years, went to Central World Plaza after learning that opponents of the PM would attend. They went because they liked the prime minister's achievements.

When he heard a man shouting for Thaksin to get out and saw police doing nothing, Chaiyasit said he put the man in a headlock in an attempt to stop him shouting. He admitted he told the man he was a police officer, because he feared the man would not follow him, so he lied that he was a policeman.

Despite Manit's insisting that the two men were not police officers, Pol Colonel Rithirong Thepchandra, investigation superintendent of Metropolitan Police Division 6, was caught on camera talking to Chaiyasit and Charan at least twice during the half-hour melee.

"I was merely curious as to what agency the two men were from," Rithirong said, when confronted by reporters yesterday.

"They told me that they were here to keep order but did not say who they were working for. So I told them to help us maintain order and not go beyond the law," Rithirong said.

Rithirong did not ask to see the two men's credentials. He dismissed suggestions that he turned a blind eye to the beatings by Chaiyasit and Charan "because it was too chaotic".

"When the situation calmed down the two men were gone. My unit is looking for them so we can bring them to justice," he said.

Questions about the identity of the two men grew rapidly yesterday after it became obvious that the large number of uniformed police at the scene did virtually nothing to stop the pair punching and slapping demonstrators.

Television footage showed police clearing the way for the two to drag the demonstrators to waiting police cars.

The drama on Monday took place shortly after Thaksin presided over the opening of the Digital Thai Knowledge Park then left the shopping complex.

The bashings prompted about 30 anti-Thaksin supporters to file a complaint with Dej-Udom Krairit, president of the Law Society, claiming police failed to intervene in clashes at Central World Plaza.

They said that by standing back and watching the violence, the police indirectly backed Thaksin supporters to attack the PM's opponents, Dej-Udom said.

The Law Society would file a lawsuit against police at the scene, he said.

The People's Alliance for Democracy has given the police seven days to arrest the attackers - or it will stage a new round of demonstrations in protest.