An anti-government protester sits on a main road as riot police stand guard at a barricade near the Government Complex in Bangkok. Picture: Kerek Wongsa

Bangkok - Thousands of riot police were deployed in the Thai capital on Friday to clear areas occupied for weeks by opposition protesters, tearing down makeshift barricades around the besieged government headquarters.

The operation in Bangkok marked an unexpected shift in tactics by Prime Minister Yingluck Shinawatra's government after months during which the demonstrators have often appeared to be more in control of the city than the authorities.

Apparently emboldened by dwindling protester numbers and the failure of the opposition to have a recent election nullified by the courts, the government attempted to regain the upper hand by reclaiming key state buildings.

Police with shields and riot helmets, some carrying rifles, met little resistance as they re-took areas around Government House, which Yingluck had been unable to use for about two months.

Security forces removed protesters' tents and ripped down their makeshift defences built from barbed wire, sandbags and piles of rubber tyres, according to AFP reporters.

But it was unclear if the operation was a success as demonstrators were later seen rebuilding barricades. Police also pulled back from an occupied government complex in the north of the city before they could clear the area.

Thailand remains deeply divided more than seven years after a controversial military coup ousted then-premier Thaksin Shinawatra - Yingluck's brother.

The kingdom has been periodically rocked by mass demonstrations by rival protest groups broadly allied or opposed to the tycoon-turned-politician, who wooed rural voters with policies such as affordable healthcare and micro-loans.

Thaksin is hated by many southerners, middle class Thais and members of the Bangkok elite who see him as authoritarian, corruption and a threat to the revered monarchy.

The deployment of security forces revived memories of a bloody crackdown on mass pro-Thaksin “Red Shirt” rallies in 2010 under the previous government, using armed troops backed by armoured vehicles.

Unlike on that occasion, when scores were killed, there were no serious injuries in Friday's operation, which targeted an area of the government district where few demonstrators remained, rather than the main rally stages in the heart of the commercial district.

Labour Minister Chalerm Yubamrung, responsible for overseeing a state of emergency imposed in the capital, said officials would return to work at Government House on Monday.

He said sling-shots, illegal drugs and bomb-making materials were discovered at the rally site.

“Protesters - you should return home,” Chalerm said in a televised national address from the government headquarters.

“If you're still stubborn we will gently enforce the law,” he added. “The police are ready to disperse protesters but the prime minister told us not to use force to avoid loss of life.”

So far the authorities have not announced any plan to clear major intersections in the retail and hotel districts that have become the main focus of the rallies in recent weeks as part of what protesters have described as the “Bangkok shutdown”.

In any case attendance has fallen sharply, with most sites nearly deserted for much of the day and several thousand people joining the rallies in the evenings.

There has been a series of grenade attacks and shootings in the capital - part of a wave of political violence linked to the protests that has left at least 10 people dead and hundreds injured.

National Security Council chief Paradorn Pattanatabut said the authorities planned to re-take several other government buildings including the interior ministry, and arrest protest leaders.

He described the operation as “successful”, pointing to the weapons seizure.

“Although protesters came back they are not intruding into Government House,” he said.

But a spokesman for the anti-government movement, Akanat Promphan, criticised the operation as a “total failure”.

“We will continue to demonstrate until we win,” he added. “We will resist any attempt to reclaim rally sites using non-violence.”

The demonstrators want Yingluck to stand down to make way for an unelected “People's Council” to enact reforms to tackle corruption and alleged vote-buying before new polls are held.

Yingluck's government held a general election earlier this month in an attempt to calm the civil strife but the opposition boycotted the vote.

Demonstrators prevented 10 000 polling stations from opening in the election, affecting several million people.

Yingluck's opponents say her government is controlled by her brother Thaksin, who fled overseas in 2008 to avoid jail for a corruption conviction and now lives in Dubai.

Pro-Thaksin parties have won every election for more than a decade, most recently in 2011 under Yingluck, helped by strong support in the northern half of the kingdom.

On Wednesday, in a boost to the government, the opposition lost a legal bid to nullify the February election. Poll re-runs are set for April 27 for constituencies where voting was disrupted. - AFP