BANGKOK: Thailand's "Red Shirt" demonstrators defied the government and vowed to keep up their protests Sunday, after the country's worst political violence in decades left 19 people dead and over 800 injured.

Protest leaders, who have promised to maintain their campaign until the government dissolves parliament and calls fresh elections, demanded Prime Minister Abhisit Vejjajiva step down and leave the country.

Fourteen civilians, including a Japanese TV cameraman, and five soldiers were killed in Saturday's crackdown on the red-shirted supporters of fugitive ex-premier Thaksin Shinawatra in Bangkok, the emergency services told AFP.

The violence erupted when troops tried to clear one of two sites in the centre of the capital occupied by the protesters for the past month. Soldiers fired in the air and used tear gas while the Reds responded by hurling rocks.

As the clashes intensified gunshots echoed around the city and both sides accused the other of using live ammunition. Emergency services said two protesters were killed by gunshot wounds to the head.

At one stage protesters overwhelmed and captured an armoured personnel carrier, while army spokesman Sunsern Kaewkumnerd said government weapons had fallen into the hands of the demonstrators.

The army later retreated, calling for a truce with the demonstrators, who were holding five soldiers hostage. Thousands of protesters remained on the streets at the two main protest sites on Sunday.

"Abhisit must leave Thailand," Reds leader Veera Musikapong told supporters. "We ask all government officials to stop serving this government."

"We call for Abhisit to resign immediately," added Nattawut Saikuar, another protest leader. He said the protesters would later hold a mourning ceremony for the dead and vowed that those killed "did not die in vain".

Government spokesman Panitan Wattanayagorn said an investigation had been launched into the violence and that negotiations were under way to bring about a resolution to the stand-off without further unrest.

"The prime minister's secretary is coordinating with protest leaders to solve the situation and would like protesters to stay put," he said.

The Thomson Reuters news agency said one its journalists, Japanese cameraman Hiro Muramoto, died after being shot in the chest during the protests.

Tokyo urged Bangkok to investigate the death and called on the Thai government to ensure the safety of Japanese nationals. Related article: Japan urges probe into journalist's death

The unrest marked Thailand's worst political violence since 1992 and the United States urged both sides to show restraint.

The mostly poor, rural Reds say the government is illegitimate as it came to power with military backing in 2008 after a court ousted Thaksin's allies from power.

The protesters called on the country's revered King Bhumibol Adulyadej to intervene to prevent further bloodshed.

"Did anybody inform the king that his children were killed in the middle of the road without justice?" Reds leader Jatuporn Prompan said. "Is there anyone close to him who told him of the gunfights?"

Although he has no official political role, the hospitalised king is seen as a unifying figure. And during a 1992 uprising he chastised both the military and protest leaders, effectively bringing the violence to an end.

"It's frightening. We heard explosions and people were running all around," said Sharon Aradbasson, a 34-year-old Israeli tourist in the city's historic area near the Khaosan Road backpacker district.

Thai flags, red roses and incense sticks were placed on pools of blood where protesters were killed or wounded.

Subdued tourists mingled with protesters below buildings pocked with bullet holes, some taking photos, a few yards from a clump of ruined cars with their windows smashed in. Shopkeepers nearby swept up glass from a shattered door.

Abhisit offered his condolences over the deaths but refused to bow to the protesters' calls to resign.

"I and my government will continue to work to resolve the situation," he said in a televised address to the nation.

Arrest warrants have been issued for many of the senior leaders but so far none is reported to have been taken into custody.

It was the latest chapter in years of political turmoil in Thailand pitting Bangkok's ruling elite against the mainly working class Reds.

The country has been riven by political tensions since a bloodless coup ousted premier Thaksin in 2006.