Armoured vehicles and van loads of troop reinforcements are converging on an anti-government protest camp in Bangkok, raising fears of an imminent crackdown.
Thailand's government is taking decisive action against "Red Shirt" protesters and last-minute peace talks are over, a senator said today as military forces advanced on their rally site.
Jourmalists and photographers at the scene of the long-running demonstration in the Thai capital say they have seen up to 12 armoured personnel carriers (APCs) with machine guns in the Silom business district.
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An AFP photographer said troops wearing balaclavas and carrying weapons and riot shields had been dropped off nearby.
Hundreds of armed police were forming lines in Sukhumvit Road, a main thoroughfare leading into the protest zone, backed up by some 20 police vans on the roadside.
The Reuters news agency is reporting that one of the anti-government protest leaders is expecting a battle between security forces and Red Shirt activists.
"We're asking everybody to be ready for a crackdown because armoured personnel carriers are beginning to move in (to the area)," said Nattawut Saikua.
Fears of military crackdown
But the Thai army's spokesman has refused to reveal whether a crackdown was imminent.
"I will not answer any questions," said Sunsern Kaewkumnerd.
Local hospitals are said to be on full alert in case of further clashes between the army and protesters who have occupied a number of sites around Bangkok for the past six weeks.
There are reports the US embassy in Bangkok has warned its citizens to stay off the city's streets because of the heavy military presence.
The Red Shirts have defied a government deadline - set on Monday - to disperse or face two years in jail.
On Tuesday night, the protesters said they feared a crackdown would be launched at dawn, after the government ruled out negotiations until the demonstrators abandoned their heavily fortified rally base.
Deadly clashes on streets
Security forces have battled with protesters since last Thursday, attempting to seal off the sprawling protest site, and triggering clashes on the perimeter that left 39 dead and hundreds injured.
The violence, which eased on Tuesday with only sporadic gunfire, turned parts of the city of 12 million into no-go zones as troops used live ammunition against protesters, who fought back mainly with homemade weapons.
"There's a very significant reinforcement of troops on Silom," said a police officer from Lumpini district near the protest site.
Asked whether a crackdown was under way he said: "Normally military will not inform police because this is a military operation alone."
There are still about 5,000 protesters - including hundreds of women and children - at the fortified site despite the fighting and a campaign for them to return home.
UN calls for negotiations
Government spokesman Panitan Wattanayagorn said the campaign to contain the protest was progressing well but that the public "must be patient as the operation is taking time".
"The operation will go ahead but the government will try to avoid confrontation and if there are losses they will be minimised," he said yesterday.
Amnesty International has accused the army of "reckless use of lethal force" in its campaign to seal off the protest zone.
UN High Commissioner for Human Rights Navi Pillay called on both sides to negotiate an end to the violence, saying there was a high risk it could "spiral out of control" after the expiry of Monday's deadline.
"To prevent further loss of life, I appeal to the protesters to step back from the brink, and the security forces to exercise maximum restraint in line with the instructions given by the government," she said.

