Anti-government protesters again fought security forces on Monday, a day after violent clashes erupted and protest leaders issued an ultimatum to the Prime Minister to resign.
Police used tear gas to repel protesters hurling sticks and other projectiles at security forces guarding government headquarters in Bangkok's old quarter, which houses the Prime Minister's offices.
Thai protesters battle into the night
RAW VIDEO: Anti-government protesters in Bangkok try to bulldoze barriers around government buildings as night falls.
The protesters had set Sunday as ''Victory Day'' but failed to seize any government offices, despite violent clashes with police.
After the government asked residents to stay indoors between 10pm and 5am, for their own safety, protesters renewed their efforts to break through heavily guarded security barriers.
Prime Minister Yingluck Shinawatra appears to have a dwindling number of options to end the crisis that has left at least five people dead, scores injured and crippled her administration. She is under intense pressure to dissolve parliament and call elections to defuse tensions.
She said on Monday the military would remain neutral in the political crisis, and she would ''open every door'' to pursue talks with protesters, adding that police would not use force against them.
On Monday, the United Nations closed its main office in Bangkok, dozens of schools were closed and many public servants stayed away from work after a call for a nationwide stop-work by protest leader Suthep Thaugsuban, deputy prime minister in the previous government.
In a meeting late on Sunday night, co-ordinated by Thailand's army chief Prayuth Chan-ocha, Mr Suthep told Ms Yingluck she must hand over power to a so-called ''people's assembly''.
''I told Yingluck that this meeting, which will be the first and last one, is not for any discussion or negotiation but it's a meeting to tell her that the people want power back, and people will manage the power by themselves,'' he told supporters.
Mr Suthep said he told the Prime Minister that a people's assembly would create a new electoral system and then call elections.
As the crisis worsened last week, Ms Yingluck had repeatedly offered to talk to Mr Suthep but insisted she would not stand down, or seek a new mandate at the polls.
''I will not flee anywhere. I may be a woman but I have the courage to face all possible scenarios,'' Ms Yingluck, the country's first woman prime minister, insisted on Sunday.
If the situation continues to worsen, Thailand's powerful armed forces could intervene before the 86th birthday of the greatly revered King Bhumibol Adulyadej on Thursday, a sensitive day in Thailand. The military has staged 18 coups, or attempted coups, since the 1930s.
The government's downfall would provoke the pro-government red shirts mass movement and could cause the unrest to spread from Bangkok to provincial regions in this country of 62 million people.
To defuse tensions, on Sunday red shirt leaders told their supporters to go home, after a night of violence around a suburban stadium where about 70,000 supporters had gathered to show their support for Ms Yingluck.
More than 3000 troops were deployed in Bangkok to help police protect government offices.
Most protesters are middle-class Bangkok residents and people brought in from opposition Democrat Party strongholds in the south of the country.
The protests were organised after government MPs tried to pass an amnesty bill in parliament that would have allowed Ms Yingluck's billionaire brother Thaksin Shinawatra to avoid a two-year jail sentence for corruption.
Thaksin, a former prime minister who has been living in exile since being toppled in a bloodless coup in 2006, has the strong support of Thailand's rural majority.