With a flurry of punches and kicks, hundreds of Thai "Red Shirts" undergo self-defence drills as they mobilise to protect the embattled government, stoking fears of a dangerous new phase of civil conflict.
While far from a battle-ready militia, the ranks of sun-weathered rice farmers brim with determination to prevent opposition protesters in Bangkok toppling Prime Minister Yingluck Shinawatra.
Drawn from the poor but populous north and northeast, the Red Shirts broadly support ousted former premier Thaksin Shinawatra -- Yingluck's elder brother.
Their rhetoric has crescendoed over the last few weeks, matching an intensifying barrage of legal challenges that could lead to Yingluck's removal from office.
In anticipation of her fall, the Red Shirts say they will bring hundreds of thousands of supporters to a Bangkok suburb on Saturday for a two-day rally.
The move looks likely to raise the stakes in a six-month political crisis that has left 24 people dead and hundreds wounded in grenade attacks and shootings, often targeting protesters.
A military crackdown on Red Shirt rallies in Bangkok against the previous government in 2010 left scores dead and parts of the city's commercial centre smouldering.
The backdrop is an eight-year struggle between a royalist establishment -- supported by the judiciary and the military -- and Yingluck's family, which has traditionally enjoyed strong support in the northern half of Thailand.
- 'Lion-hearts' -
"We have lion hearts... we are real fighters," local Red leader Kwanchai Pripana told AFP on the sidelines of the training camp in the movement's heartland of Udon Thani on Thursday.
At the camp, around 500 -- mainly middle-aged -- men and women gamely rehearsed Muay Thai boxing moves and parade drills despite the sapping heat.
They have shed their red T-shirts for new black uniforms, in symbolic mourning over a court decision to nullify a February general election disrupted by protesters.
Kwanchai said 40,000 volunteers have already signed up to act as guards for Red Shirt protests, with several further rounds of training planned across the northeastern region of Isaan.
"We are building our strength to learn how to defend ourselves," he said, stressing the volunteers would be unarmed. "If they kill us this time, when one dies, one thousand Red Shirts will be born."
Kwanchai was shot several times at his home in January in what was believed to have been a politically motivated attack. He now periodically needs a wheelchair and has limited use of his right arm.
Still, with fellow firebrand Suporn Attawong -- dubbed "Rambo Isaan" -- he organised the training camp for the "Democracy Protection Volunteers".
Without a swift cooling of tempers on both sides of Thailand's bitter divide, analysts warn more violence lies ahead.
If Yingluck falls, the Red Shirts could seize official buildings and block roads in their strongholds, potentially prompting the army to act to restore order, according to Matthew Wheeler of the International Crisis Group think-tank.
"The prospects for the country look grim in the near term. People feel it's going to get worse before it gets better," he added.
Observers say the Shinawatra family has been holding back its trump card to use in the event Yingluck falls.
She faces neglect of duty charges linked to a loss-making rice subsidy scheme and allegations of abuse of power over the transfer of a top security official.
"Once Thaksin uses the Reds, it may be impossible to control them," said Paul Chambers, director of research at the Institute of South East Asian Affairs at Chiang Mai University.
The movement could become "a sort of bucking bronco," he added.
- Reds rising? -
Thaksin, a billionaire tycoon-turned-politician, fled overseas in 2008 to avoid jail for a corruption conviction, but he is seen as pulling the strings behind his sister's premiership and is accused by opponents of nepotism and rampant corruption.
His critics say he uses taxpayers' money to buy the loyalty of rural voters through populist policies.
The Red Shirts fear that the political and economic clout they have gained since Thaksin's emergence in 2001 will now be taken away by Thailand's wealthy establishment.
Broadly representing the Bangkok elite and middle-classes as well as parts of the Thai south, the opposition wants to install an unelected leader to oversee vaguely defined reforms aimed at tackling corruption and rooting out Thaksin's influence.
Sheltering from the baking sun in a covered parade ground in Udon Thani, the Red Shirt volunteers said the time has come to defend their elected premier and their democratic stake in the kingdom's future.
"I voted for Yingluck, now I want to protect her," said Pradit Viengdindam, a 54-year-old street vendor who recently bought life insurance in case his two children are left with no father.
"We need to fight now or the power of our vote will be taken away forever by the elite."