Thai troops opened fire on protesters on Friday after a military lockdown of their rally site in the heart of the capital sparked fierce clashes that left three people dead and at least 46 wounded.
Security forces moved to regain control of a road close to the Suan Lum Night Bazaar, a popular spot with tourists, after "Red Shirt" demonstrators spilled out of their fortified rally base, which was under siege by troops.
The protesters, who are trying to bring down the government of Prime Minister Abhisit Vejjajiva, threw stones, used slingshots and launched fireworks at the troops.
Three journalists, one of them a Canadian with the France 24 television channel, were shot in their legs and wounded while covering the violence.
Soldiers used tear gas against the demonstrators, who set fire to piles of tyres in the road, torched an empty police bus and vandalised army vehicles as well as a water cannon as part of their efforts to disrupt the lockdown.
Volleys of gunfire rang out through the afternoon, sending people fleeing in panic. At one point troops fired directly at protesters and then advanced up a road shooting into the air, according to an AFP reporter.
Two of the dead appeared to be Red Shirt security guards, said the director of the hospital where they were taken, adding that one victim was shot in the temple and the other in the chest.
The third fatality was a 32-year-old man who died earlier of gunshot wounds.
At least 33 people have been killed and about 1,000 injured in Bangkok in a series of confrontations and attacks since the protests began in mid-March.
The mood was tense inside the encampment, which has been fortified with razor wire, truck tyres doused with kerosene and sharpened bamboo poles.
"Abhisit has already started civil war," top Red Shirt Nattawut Saikuar told reporters.
"We urgently demand the government withdraw the military and stop all violence," he said. "I don't know how we can survive tonight if Abhisit does not agree to a ceasefire. We hope that Abhisit does not want war."
The Reds consider Abhisit's government illegitimate because it came to power in a 2008 parliamentary vote after a court ruling ousted elected allies of their hero, former premier Thaksin Shinawatra, who was unseated in a 2006 coup.
Thaksin, who lives in self-imposed exile to avoid a jail term at home for corruption, called on the government to pull back troops and restart negotiations with the demonstrators.
"The government's actions clearly constitute grave infringement of human rights and criminal offences for which the prime minister, the deputy prime minister and all concerned must be responsible," Thaksin said in a statement.
Defence Minister General Prawit Wongsuwon said the military operation was meant to force the movement's leaders back to talks with the government.
Around the protest area, which extends for several square kilometres, soldiers blocked roads and set up checkpoints to seal off the area. The city's elevated Skytrain was suspended before nightfall.
The army had warned Thursday it would deploy snipers around the Reds' protest site and blocked roads to prevent more demonstrators joining thousands who have occupied a large area of central Bangkok for two months.
A renegade general allied with the Reds was fighting for his life after being shot late Thursday close to the protest site. His supporters said he was targeted by a sniper. The army denied any involvement in the incident.
Major-General Khattiya Sawasdipol, who had been accused of trying to stymie government moves to reconcile with the protesters, was unconscious in the intensive care unit of Vahira hospital with a head wound.
He had a "low" chance of survival, said Chaiwan Charoenchokethavee, the hospital director.
The violence came after Abhisit shelved a plan to hold early elections in November after reconciliation efforts broke down.
The mostly poor and working class Reds initially agreed to enter the peace process but efforts to reach a deal that would see them go home eventually broke down.
Almost one-third of the country, including Bangkok, is now under emergency rule.