Thousands of Red Shirt protesters remained have camped in the historic heart of the capital, which will be the starting point of Saturday's march that will loop the capital and wind through Bangkok's central business district.
"It will be a massive caravan," said Jatuporn Prompan, a leader from the movement formally known as the United Front for Democracy against Dictatorship. "Protesters will travel around Bangkok on thousands of vehicles."
The protesters want Prime Minister Abhisit Vejjajiva to dissolve Parliament and call fresh elections - a demand he has repeatedly rejected. Abhisit has been sleeping and working from an army base for the past week to avoid demonstrators.
Protest leaders have increasingly portrayed the demonstrations that started last Sunday as a struggle between Thailand's impoverished, mainly rural masses and a Bangkok-based elite impervious to their plight. The group largely consists of supporters of former Prime Minister Thaksin Shinawatra, who was ousted by a 2006 military coup for alleged corruption, and pro-democracy activists who opposed the army takeover.
In an attempt to dramatize their demands, thousands of Red Shirts lined up Tuesday to donate blood to their cause. Leaders claimed they collected 300,000 cubic centimetres of blood that were transferred into dozens of large plastic jugs.
Most of the blood was splattered at Abhisit's office, at the headquarters of his ruling party and at his private residence.
Protest leaders say they have 15 jugs of blood leftover and plan to use it to create a massive work of art.
"Artists and Red Shirts will be invited to partake in a blood painting," Jatuporn said. They plan to unfurl a giant white cloth on which supporters will be invited to paint pictures, scrawl poems and express political statements.
"The theme of this artwork will be the history of the people's fight for democracy," Jatuporn said.
Thaksin is popular among the rural poor for his populist policies. They believe Abhisit came to power illegitimately with the connivance of the military and other parts of the traditional ruling class and that only new elections can restore integrity to Thai democracy.
Abhisit said Thursday that the blood-spilling antics tested the limits of the law - and were testing his patience. He reiterated the government's stance that the protests will be allowed to continue as long as they remain peaceful.
"Actions like drawing blood, pouring it and throwing - strictly speaking are not all legal," Abhisit said, adding that protesters were also not allowed to block city streets and prevent government employees from entering their offices.
The size of the protest peaked Sunday at some 100,000 demonstrators, but has decreased by about half since then.
