Tony Birtley reports from Bangkok on the military crackdown that scattered protesters

Curfew has been imposed in Bangkok and several provinces of Thailand in response to widespread violence and vandalism triggered by a military operation to retake the capital's commercial district from opposition red-shirt protesters.

Six important red-shirt leaders surrendered to the police after soldiers breached barricades surrounding the protest zone in the upscale Rachaprasong shopping district early on Wednesday.

Several prominent buildings across the city were subsequently set ablaze by their followers in spite of appeals for restraint.

At least six people are known to have died in Wednesday's unrest.

The government has imposed a curfew from 8pm (1300GMT) to 6am (2300GMT) in Bangkok and extended it to 24 other provinces.

It said military operations would continue overnight and security forces had been authorised to shoot looters and arsonists.

Abhisit Vejjajiva, the prime minister, said in a televised address late on Wednesday that he believed his government could soon "end the problems and return the country to peace and order once again."

Red shirts' fury

The red shirts set several buildings on fire, notably the Bangkok stock exchange, as they retreated from their protest camp. Central World, the second largest department store in Southeast Asia, was destroyed in a blaze.

The red shirts also attacked the offices of state-run Channel 3, setting it on fire, forcing the evacuation of its executives by helicopter. Police rescued the rest of the staff.

The English-language Nation and Bangkok Post newspapers evacuated their staff after threats from the red shirts.

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  Crackdown in Thailand

A large office building down the street from the Bangkok Post office was set alight.

Unrest also spread to Thailand's rural north and northeast, the protesters' heartland.

Local media reported protesters set fire to government offices in Udon Thani and vandalised a city hall in Khon Kaen.

Udon Thani's governor asked the military to intervene. TV images showed troops retreating after being attacked by mobs in Ubon Ratchathani.

Tony Birtley, Al Jazeera's correspondent in Bangkok, said violence had spread to some extent.

"There have been outbursts of violence in several places in the north and northeast," he said.

"A contact of mine phoned me from Chiang Mai [in the north] saying that fire engines were set alight, property was destroyed and barricades were set up there, so the violence is spreading."

Against this backdrop, Thaksin Shinawatra, the country's ousted prime minister whom many of the red shirts support, said he feared a military crackdown could lead to guerrilla warfare across the country.

"There is a theory saying a military crackdown can spread resentment and these resentful people will become guerrillas," he told the Reuters news agency by telephone.

Thaksin, who is accused by the government of bankrolling the protests and inciting unrest, denied he had undermined peace talks, saying he was not the "mastermind of the terrorists".

But Tim Forsyth, a South Asia expert based in the UK, cast doubt on Thaksin's claims of innocence.

"Unlike previous demonstrations involving the red shirts, this time they have had a small proportion of highly armed specialised paramilitary people amongst them," he told Al Jazeera.

"They have also had a very clear intention of trying to embarrass and bring down the current government.

"This suggests that Thaksin may well be behind all this because after all he wants his money unfrozen and he wants to influence Thai politics again."

Military assault

Wednesday's crackdown began with about 100 soldiers armed with automatic rifles and shotguns, along with several machinegun-mounted armoured personnel carriers, breaching the red shirts' barricade at the southern end of their protest site in Bangkok's Rachaprasong neighbourhood.

The armoured vehicles repeatedly rammed the barricade, made up largely of tyres, sharpened bamboo poles and razor wire, before breaking through the flattened structure.

Red shirts lit fuel-soaked tyre barricades in an attempt to defend their protest camp [AFP]

Al Jazeera's Wayne Hay, reporting from the protest zone, said troops moved quickly through the first kilometre of the site, towards the main stage where the leaders of the red shirts were believed to be.

At least two bodies - suspected to be of slain red-shirt guards - were seen being removed from the area, he said, and the Thai Red Cross appealed for blood donations.

Jongjet Aoajenpong, the head of a local hospital, was quoted by the AFP news agency as saying that an Italian journalist was shot in the stomach and "died before arriving".

Al Jazeera's Birtley said the raid on the protest camp was a relative success for the military.

"This was one of those feared operations that people believed that if the military came in heavy handed, hundreds of people could be killed and injured," he said.

"That hasn't happened. However, there are many problems and grievances that exist for these people and that will have to be addressed by any Thai government in the future."

Source: Al Jazeera and agencies