Thailand took a tough stand against thousands of anti-government protesters today, rejecting demands for UN-supervised talks and calling on their leaders to surrender after deadly clashes with troops.

The hardline comments from the Thai government doused hopes of a compromise to end three days of fighting that has killed at least 29 people, all civilians, and wounded 221, trapping residents in homes and raising the risk of a broader conflict.

Nattawut Saikai, a protest leader, called for a ceasefire and UN-moderated talks. "We have no other condition. We do not want any more losses," he told supporters.

But the government swiftly dismissed the offer. "If they really want to talk, they should not set conditions like asking us to withdraw troops," said Korbsak Sabhavasu, the prime minister's secretary-general.

Authorities declared a state of emergency in five more provinces as fighting showed signs of spreading to the north and north-east.

A political scientist at Chulalongkorn University, Vienrat Nethito, said rejection of any ceasefire talk was ominous. "This pretty much guarantees fighting will continue and the city will be even closer to the brink of civil war."

In Bangkok, many residents stayed indoors today or stocked up on food and other supplies as fighting raged.

The heaviest fighting took place in the Bon Kai area of Rama IV, a main artery to the business district. Troops and snipers fired machine guns as protesters hurled petrol bombs and burned walls of kerosene-soaked tyres.

One protester was shot in the head by a sniper, a witness said. By afternoon, as clashes intensified, a grenade was tossed at troops, who responded with gunfire that scattered the demonstrators into nearby alleys.

Some wounded protesters were taken to hospital on the back of motorcycles, witnesses said, as medical rescue workers were either blocked by the military or too scared to enter the scene of clashes after two medical workers were killed in the clashes.

The protesters had been demanding the resignation of the British-born, Oxford-educated prime minister, Abhisit Vejjajiva, whom they accuse of colluding with Thailand's royalist elite and meddling with the judiciary to bring down previous elected governments.

"I will stay here. We will not flee," Jatuporn Prompan, a protest leader, told supporters in their 1.2 square mile encampment where at least 5,000 people, including women and children, are barricaded behind walls of tyres, poles and concrete.

Some women, children and the elderly are trickling into a nearby Buddhist temple for safety. The government is seeking co-operation with protest leaders to dispatch Red Cross workers and other human rights volunteers to persuade people to leave.

Analysts and diplomats said the military appeared to have underestimated the resolve of the protesters who have been barricaded in a district of luxury hotels and shopping malls for six weeks.

The mostly rural and urban poor protesters, supporters of the ousted premier Thaksin Shinawatra, accuse the military-backed government of colluding with the royalist elite and meddling with the judiciary to bring down previous Thaksin-allied governments.

No soldiers have been identified in the official death toll. Two rescue medical workers have been killed and five journalists shot, though one was not wounded because the bullet deflected off his flak jacket.

A witness said that a young man walking in the street near Victory Monument, where clashes took place on Saturday, was shot in the head by a sniper's bullet. He did not appear to be a protester.

Many protest leaders face terrorism charges that carry a maximum penalty of death, raising the stakes in a two-month crisis that has paralysed parts of Bangkok, stifled south-east Asia's second-biggest economy and decimated tourism.

The US embassy has offered to evacuate families and partners of US government staff based in Bangkok on a voluntary basis, and urged its citizens against travel to Bangkok.

The government's strategy of starving protesters out of their encampment was shows signs of having an effect. Supplies of food, water and fuel were starting to run short as the redshirt delivery trucks were blocked. But protesters said they still had enough to hold out for days.