Thousands of Thai demonstrators spilled their blood in front of the government's administrative compound in Bangkok Tuesday in a symbolic protest against its 'elitist' leader Prime Minister Abhisit Vejjajiva and his cabinet.

The United Front for Democracy against Dictatorship (UDD), also called the red shirts, have been protesting in Bangkok since Sunday to force Abhisit to resign and call for new elections.

Their stated aim is to pave the way for a political comeback for their de facto leader - ousted former premier Thaksin Shinawatra.

After collecting blood from thousands of supporters, the protestors poured about 50 containers, or about 275 litres of blood, in front of the six entrances of Government House.

'When Abhisit comes to work he will have to drive over the people's blood,' UDD co-leader Nattawut Saikuer said. 'The blood of the red shirts is warm, but the blood of Abhisit is cold.'

On Monday, Abhisit rejected the UDD's ultimatum to resign by noon.

Peeved, the UDD leaders vowed to collect blood from their 100,000 followers to throw on the entrance to Government House Tuesday as part of a curse against Abhisit and his cabinet.

About 10,000 donated blood early Tuesday.

Abhisit, Thailand's articulate Oxford-educated premier since December 2008, is a prime target of the red shirt leaders' rhetoric.

They argue that Abhisit came to power illegitimately, with the backing of the military, and is the puppet of Bangkok's 'amarat', a vague Thai term describing rule by bureaucrats.

Abhisit came to power by a parliamentary process after the dissolution of the former People's Power Party in December 2008, following the party's condemnation for electoral fraud in the December 2007 polls.

The UDD marched on the Democrat Party headquarters in Bangkok to spill more blood there after their bloodletting at Government House.

So far the UDD protests have been violence-free.

The government, which has 42,000 soldiers and police on hand to maintain the peace in Bangkok, has thus far treated the protests gingerly.

'If it is a peaceful protest, you have to allow it,' acting government spokesman Panitan Wattanayagorn said.

The UDD last week promised to draw 1 million protestors to Bangkok to topple the current government. An estimated 100,000 showed up.

The government has placed Bangkok and seven surrounding provinces under the Internal Security Act between March 11 and 23, empowering authorities to prohibit protests in sensitive areas and detain perpetrators of violence for up to a year.

'Our first priority is to make sure no one gets hurt or injured,' Panitan said. 'Thailand is a bit strange in that if one person is killed or injured in a political rally that is very difficult to explain to the public.'

Thaksin, who was prime minister from 2001 to 2006, continues to hold sway over millions of the country's urban and rural poor thanks to the populist policies he implemented during his two-term premiership. He also enjoys support from a broad spectrum of society intent on changing the status quo.

Thaksin, who was toppled by a coup in September 2006 has been living in self-imposed exile, mostly in Dubai, since August 2008 to avoid a two-year jail sentence for abuse of power.