Thai protesters have stood their ground in Bangkok, defying a vow from PM Abhisit Vejjajiva to use the military to stop them toppling his government.Several hundred protesters are gathering in another part of the city.
One protest leader said Thailand was close to "civil war" after clashes in Bangkok between protesters and soldiers that have left at least 25 people dead.
Mr Abhisit is set to impose a curfew in Bangkok and has postponed the new school term in the city for a week.
The fighting flared on Thursday as the army moved to isolate a fortified protest camp.
Thousands of people who say Mr Abhisit came to power undemocratically remain behind makeshift barricades of rubber tyres, sandbags and bamboo stakes in the Ratchaprasong commercial district.
The protesters are known as red-shirts, after the colour they have adopted.
They want the prime minister to step down to make way for new elections.
Red-shirt leaders have been calling for reinforcements, but protesters coming from elsewhere in the country have been unable to breach the military cordon, and are congregating nearby.
Several hundred red-shirt suppporters have gathered around a mobile stage set up in central Bangkok's Klong Toey area, and protest leaders have called for a rally at another mobile stage in the north of the city.
Army 'prepared'
In a televised address on Saturday, Mr Abhisit said the army would not back down in its operation to clear the protesters.
"We cannot leave the country in a situation where people who don't obey the law are holding hostage the people of Bangkok, as well as the centre of the country," he said.
"We can't allow a situation where people set up armed groups and overthrow the government because they don't agree with it."
Mr Abhisit has said that a few armed "terrorists" are among the protesters.
An army spokesman said the military was planning to enter the protesters' camp if they did not disperse, but gave no timetable.
"There is a plan to crack down on Ratchaprasong if the protest does not end," said the spokesman, Col Sunsern Kaewkumnerd.
"But authorities will not set a deadline because without effective planning there will be more loss of life."
The BBC's Chris Hogg in Bangkok says the army's actions are like squeezing a balloon full of water - they are just pushing protesters into a different part of the city.
Black smoke drifted into the air over Bangkok on Sunday morning but the streets were mostly quiet after three days of fierce battles that saw soldiers fire live rounds and rubber bullets at protesters who threw stones, petrol bombs and shot fireworks in return.
The army has declared live fire zones in some areas as it attempted to cut off the camp from supplies and reinforcements.
Around 200 people have been injured since the latest violence broke out on Thursday, and 27 people have been sent to jail, each given six-month sentences. All the fatalities have been civilians.
More than 50 people have been killed and at least 1,500 wounded in total since the protests began in mid-March, Thai officials have said.
Despite claims by the Thai government that the situation was under control and its soldiers had only fired in self-defence, army snipers have been accused of targeting protesters. Footage from Bangkok on Saturday showed red-shirts dragging gunshot victims to safety.
The violence escalated on Thursday after a renegade general who supports the protests was shot in the head by an unknown gunman.
Gen Khattiya Sawasdipol, better known as Seh Daeng (Commander Red), is in a critical condition.
National divisions
The latest clashes have raised questions about the stability of Thailand, South-East Asia's second-largest economy.
"The current situation is almost full civil war," said one of the protest leaders, Jatuporn Prompan. "I am not sure how this conflict will end."
Many of the protesters are from poor rural areas in northern Thailand where support is still strong for former Prime Minister Thaksin Shinawatra, who was ousted in a 2006 coup.
They say Mr Abhisit was put into power in a parliamentary vote by an alliance of the Bangkok elite and the military and want him to dissolve parliament and call fresh elections.
He had offered polls in November - but the two sides failed to agree a deal because of divisions over who should be held accountable for a deadly crackdown on protests last month.
Mr Thaksin has called on the government to withdraw troops and restart negotiations. He is living abroad to avoid a jail term on a corruption conviction.
