Nearly 3,000 flag-waving anti-government protesters massed in front of Thailand's Interior Ministry on Tuesday, intensifying pressure on Prime Minister Yingluck Shinawatra a day after they stormed compounds of two other ministries.
The protesters defied a tough security law imposed across Bangkok late on Monday to control tens of thousands of protesters rallying against Yingluck and her billionaire brother, former prime minister Thaksin Shinawatra.
Waving Thai flags and blowing whistles, demonstrators surrounded the interior, agriculture, tourism and transport ministries, ordering workers inside to leave and ratcheting up tension in the biggest street protests since 2010, when 91 people were killed in a military crackdown.
Yingluck and her ruling Puea Thai Party began a two-day confidence debate in parliament where they hold a commanding majority. The opposition has accused them of graft and trying to pass laws to white-wash Thaksin of corruption allegations, but Yingluck is expected to prevail in a vote on Thursday.
"Getting rid of the Thaksin regime is not easy," said protest leader Suthep Thaugsuban, a former deputy prime minister under the previous government, in an interview with Reuters.
Thaksin, a former telecommunications tycoon, was ousted in a 2006 military coup but has hovered ghost-like over Thai politics since fleeing the country in 2008, accused of undermining the powerful monarchy, breaching conflict-of-interest laws and sentenced in absentia to two years in prison.
He remains a populist hero among the rural masses but is reviled by much of the traditional Bangkok elite of top generals, royal advisers, middle-class bureaucrats and business leaders - who largely back the opposition Democrat Party.
After forcing their way inside the Finance Ministry on Monday and bursting through the gates of the Foreign Ministry compound, the Democrat-led protesters kept marching on Tuesday.
"Our important mission today is to surround the four important ministries of the government," Watchara Ritthakanee, a protest leader, told a cheering, whistle-blowing crowd.
The government shut and evacuated staff from ministries under siege by the protesters.
The Interior Ministry, a short walk from Thailand's top tourist attraction, the Grand Palace, was surrounded by protesters. But they did not follow through on an earlier threat to enter the building.
Its high metal fence is fortified by coils of razor wire and guarded by dozens of security men in military fatigues, apparently unarmed. Earlier, protest leaders warned staff to leave or they would storm the building, witnesses said.
Thousands of protesters tried to march to the heavily barricaded Government House, the prime minister's offices. After a 15-minute standoff with police, they withdrew to Bangkok's historic quarter. Another group marched toward the Energy Ministry, which was also evacuated.
At the Finance Ministry, more than 1,000 protesters filled a courtyard, chanting "Get out! Get out!" against the government. Many had stayed overnight, sleeping on plastic mats.
The seizing of government buildings has plunged Thailand into its deepest political uncertainty since it was convulsed three years ago by the bloodiest political unrest in a generation.
Suthep and former Prime Minister Abhisit Vejjajiva have been charged with murder and accused of allowing troops to open fire with live rounds during those 2010 protests. A year later, their Democrat Party was routed in an election that swept Yingluck to power in a landslide.
In an apparent sign of rising tension, a bomb squad removed a grenade from the grounds of a Democrat Party branch office in Bangkok, said police officer Sarun Pichitmanoh, adding that he believed it had been placed there to add to the friction.
The uncertainty is driving foreign investors out of the Thai financial markets, making the baht the second-worst performing emerging Asian currency in November. The baht has lost 2.7 percent this month, while Thai stocks have retreated about 6 percent.
The Finance Ministry is still functioning well despite its seizure by protesters, its minister said.
"Key officials are still working as normal from our backup office," Finance Minister Kittirat Na Ranong told Reuters. "So there will be no impact on the fiscal budget and important functions."
Salaries are handled by Krung Thai Bank and government bond auctions are normally managed by the Bank of Thailand, officials say.
Kittirat said he was worried about investor confidence: "There will be some impact on the economy in the current quarter if the situation continues."
Kittirat said the ministry would file a lawsuit against Suthep and investigate ministry officials who had facilitated the invasion. A warrant has been issued for Suthep's arrest.
Yingluck, 46, has remained defiant, saying she would not step down.