Abhisit Vejjajiva's threat of legal action came in his weekly address to the nation on Sunday, as red-shirted supporters of Thaksin Shinawatra, the former prime minister, regrouped around his office in Bangkok, the capital.

"I promise that in the next three to four days there will legal action taken," he said. "It is most important for the government to prove it can bring peace to the nation." Abhisit has apologised to the country and to regional leaders for having to cancel the East Asia Summit yesterday after protesters overran the summit venue at the resort town of Pattaya.

On Saturday, leaders of the 10-member Association of Southeast Asian Nations(Asean) had to be evacuated by helicopter after protesters broke into the summit venue at the Thai beach resort of Pattaya. The protesters breached police lines, smashing their way into the venue's media centre, while most of the leaders were having lunch at the adjacent Royal Cliff hotel.

Once in the media centre, the protesters paraded around with flags, blew whistles and horns, helped themselves to the snack buffet laid on for the journalists. About 100 demonstrators got as far as the driveway of the hotel.

A group of rival blue shirt-clad protesters clashed, with the red shirts, throwing stones and smoke bombs at each other about five kilometres from the venue. A Thai official said two or three people were injured in the clashes and there were reports of gun shots and an explosion.

The collapse of the summit puts more pressure on British-born Abhisit, who has pledged that his four-month-old government will heal years of political turmoil since Thaksin was ousted in a 2006 coup.

The abandoned summit - the biggest international gathering since the G20 summit in London earlier this month -grouped the Asean nations with China, Japan, South Korea, India, Australia and New Zealand.