Police tightened security in Thailand's capital on Saturday as thousands of protesters rallied outside a state telecommunications group and vowed to occupy Prime Minister Yingluck Shinawatra's office to paralyse her administration.
Faced with dwindling support, demonstrators have started to up the ante and burst into the headquarters of the army on Friday, urging it to join their side in a complex power struggle centred on the enduring political influence of Yingluck's billionaire brother, ousted prime minister Thaksin Shinawatra.
"On Sunday, brothers and sisters, we will announce our victory and our defeat of the Thaksin regime," protest leader Suthep Thaugsuban told a rally of thousands late on Friday.
By midday Saturday, several thousand were outside the offices of state-owned TOT Plc, a telecoms company.
They also plan to surround headquarters of the national and city police, Government House and even a zoo. "We need to break the law a little bit to achieve our goals," said Suthep, deputy prime minister under the previous government that Yingluck routed in a 2011 election.
Hundreds of police emptied out of buses and vans near the prime minister's office at Government House in Bangkok's old quarter. One police official told Reuters about 5,000 police would reinforce the area over the day.
Suthep's threats heighten a conflict that broadly pits the urban middle class against the mostly rural supporters of Yingluck and her brother, Thaksin.
Thaksin was removed in a 2006 military coup and convicted two years later of graft -- charges he says were politically motivated. The former telecommunications tycoon has lived abroad in self-imposed exile since 2008, but remains closely entwined with government, sometimes holding meetings with Yingluck's cabinet by webcam.
Suthep urged followers to end the "Thaksin regime" by shutting a government administrative complex on Saturday and by Sunday, moving on the ministries of labour, foreign affairs, education and interior.
The government has vowed to stay open and maintain order. "We will avoid the use of force," said Pracha Promnok, a deputy prime minister. "But if protesters attempt to enter government buildings, we may have to use our powers to stop them."
Pracha said the government can continue to function even if ministries are besieged by working from backup locations.
Suthep, a silver-haired politician from Thailand's south, just weeks ago resigned from the opposition Democrat Party, which has not won an election in more than two decades and is backed by Bangkok's royalist elite.
He has called for a "people's council," which would select "good people" to lead the country, effectively suspending Thailand's democratic system.
A defiant Yingluck has rejected that as unconstitutional and has repeatedly ruled out new elections.
The protesters have accused the government of acting above the law after senior members of the ruling Puea Thai Party refused to accept a Nov. 20 Constitutional Court ruling that rejected their proposal to make the Senate fully elected. Puea Thai has argued the judiciary has no right to intervene in the legislative branch.
The measure would have strengthened Yingluck's government by giving her strong support in vote-rich northern Thailand.
The ruling casts a spotlight on Thailand's politicised courts, which annulled an election won by Thaksin in 2006 and brought down two Thaksin-allied governments in 2008 after similar protests. Members of Yingluck's party have said the judiciary had no right to intervene in the legislative branch.
Yingluck has sought to keep her distance from the issue, never openly rejecting the court ruling and stressing that she is not head of the Puea Thai Party.
That has done little to allay the flag-waving, whistle-blowing protesters.
Democrat leader Abhisit Vejjajiva, a former prime minister, said Yingluck had "acted above the law" by rejecting the Constitutional Court. He delivered a letter to the U.S. embassy on Friday explaining why she must go.
"May our whistles be heard to Washington D.C.," Korn Chatikavanij, a senior Democrat and former finance minister, told the crowd.
The protests are the biggest since red-shirted Thaksin supporters paralysed Bangkok in April-May 2010 in a period of unrest that ended with a military crackdown in which 91 people, mostly Thaksin supporters, were killed.
The Oxford-educated Abhisit and his then-deputy Suthep both face charges of murder in connection with that unrest, accused of allowing soldiers to open fire on protesters.
Bangkok is on edge again. Since Monday, demonstrators have surrounded ministries and rallied in a commercial district and outside Yingluck's party headquarters, though the number of protesters appears to have declined steadily through the week.
Friday's brief invasion of the Royal Thai Army's headquarters, which lasted about three hours and ended peacefully, illustrates how the protesters see the military as a potential ally because of its attempts to intervene against governments led or backed by Thaksin over the last decade.
Army chief Prayuth Chan-ocha, however, told protesters not to drag the military into politics. "We hope all sides will unite and not use the army as a tool," he said.
Pro-government "red shirt" supporters plan a rally on Sunday at Bangkok's Rajamangala Stadium. "Our job is to protect democracy. We will stay at Rajamangala stadium. But if there is a coup, let us open the doors," Jatuporn Prompan, a red shirt leader, told more than 25,000 supporters late on Friday.