Bangkok  - Anti-government demonstrators in Bangkok threatened Thursday to descend on this weekend's summit of the Association of South-East Asian Nations (ASEAN) unless the Thai administration resigns.

Tens of thousands of supporters of former prime minister Thaksin Shinawatra prolonged their demonstration in the centre of the capital after a call by Thaksin for Prime Minister Abhisit Vejjajiva and three advisers to the king to resign from their posts.

A leader for the so-called Red Shirt movement, Jatuporn Phrompan, said that if these people did not quickly step down and parliament wasn't dissolved, there would be a final showdown.

"Anything can happen today or tomorrow," Jatuporn said at a rally Thursday, the Nation newspaper reported.

Rally speakers claimed senior members of the Privy Counsel, which advises the king, were behind the 2006 military coup that toppled Thaksin and ultimately allowed Abhisit to form a government four months ago.

Abhisit briskly rebuffed calls for his resignation in television appearances Thursday, calling on protestors to understand that the calls for "democracy" were a blind to further the corrupt interests of an irresponsible former leader.

"My duty is not to yield merely to people who make a loud noise or threaten to use force," he said.

The threat to the ASEAN meeting in the nearby beach resort city of Pattaya came after local Red Shirts surrounded and smashed a window of Abhisit's car Tuesday and also picketed the hotel where a cabinet meeting was taking place.

ASEAN leaders are to meet there this weekend along with their dialogue partners China, Japan, South Korea, India, Australia and New Zealand.

Abhisit vowed there would be no repeat of the window smashing because security forces would flood the area to protect the visiting leaders.

Thaksin, speaking via a video link from an undisclosed country, turned up the political temperature in Bangkok Wednesday night when he told a crowd estimated by police at 100,000 that the time had come to "make our country become a true democracy" and called on his supporters to endure "until we become victorious."

He called for all Thais to don red shirts as symbols of popular revolt.

"The fight is not about me," he said. "It's about our country, our people and the future generation. We want liberty, equality and fraternity for Thailand."

Civil servants, police and soldiers should also refuse to kowtow to the outdated establishment, he added.

The Red Shirts have vowed to continue their demonstration until at least Friday in the streets around Government House, the seat of Thailand's administration, and the home of chief royal adviser and former prime minister Prem Tinsulanonda, who speakers have vilified as the "meddling old aristocrat" who is stymieing the country's progress.

The sharp and sustained criticism of key figures in the core establishment only a step away from the king himself is unprecedented.

The Red Shirts, who have been camped outside Government House for a fortnight, take their colour to distinguish themselves from the royalist yellow of their opponents, who habitually claim to be protecting the monarchy from Thaksin and his cohorts. (dpa)