Bangkok  - Thousands of Thai protestors marched on Government House in Bangkok Tuesday in an effort to highlight the alleged illegitimacy of the current administration days before it hosts a South-East Asian summit.

An estimated 15,000 followers of the United Front of Democracy against Dictatorship (UDD) - also called the Red Shirts - joined a march from Sanam Luang (The Royal Grounds) to Government House, the seat of the administration, about 3 kilometres away.

"We cannot let the world believe that this government is a legitimate government, representative of the Thai people," UDD spokesman Jakrapob Penkair said.

Organizers vowed to keep the protest peaceful. An estimated 3,000 police posted around Government House have been ordered not to use violence against the demonstrators.

The UDD is a mirror movement to the People's Alliance for Democracy (PAD), which seized Government House for three months last year and shut down Bangkok's two airports for a week in their effort to topple the previous government led by the People Power Party (PPP).

The PAD was staunchly anti-Thaksin Shinawatra, a billionaire businessman-turned-politician who was prime minister from 2001 to 2006. Thaksin, who faces a two-year jail sentence for abuse of power, has been living in self-exile since August, 2008.

Thaksin was ousted by a military coup on September 19, 2006, but his political allies returned to power in the guise of the PPP which won the December 23, 2007, general election.

Signs that the PPP was manoeuvring to return Thaksin to power brought the PAD out in the streets in May, 2008, and they continued their protests until the party was dissolved by a Constitutional Court ruling on December 3, which found it guilty of committing fraud in the last polls.

The dissolution of the PPP paved the way for the Democrat Party, which came in second place in the 2007 polls, to form a new coalition government, in keeping with the parliamentary system. The pro-Thaksin UDD insist the Democrat-led government lacks legitimacy since the Democrats did not win the largest number of seats in the last election.

The movement is calling on the government to bring the PAD leaders to trial for damaging the country's economy last year with their protests, to amend the 2007 constitution that has undermined the power of political parties, and to dissolve parliament and call for a new election.

The protests come days before Thailand is to host the 14th Summit of the Association of South-East Asian Nations (ASEAN).

Wary of protests, the government has decided to host the regional summit in Cha-am/Hua Hin, a beach resort situated about 130 kilometres southwest of Bangkok, on February 27 to March 1.

The Red Shirts' leadership has promised not to disrupt the ASEAN summit at Hua Hin, called the "royal resort" because Thai King Bhumibol Adulyadej keeps his summer palace there.

"We support international cooperation but we cannot support a government stolen form the people," Jakrapob said.

It was unclear how many days the protestors intended to stay outside Government House.

The cabinet was meeting in Hua Hin Tuesday, instead of its usual venue at Government House. (dpa)