BANGKOK - Tensions escalated in the Thai capital on Saturday as opposition protesters tried to force their way into Prime Minister Yingluck Shinawatra's heavily guarded offices and attacked a bus carrying her supporters.
Defiant demonstrators seeking to topple Yingluck's embattled administration have besieged major state buildings in Bangkok in the biggest street protests since mass rallies in 2010 left dozens dead in a military crackdown.
The protesters - a mix of royalists, southerners and the urban middle class sometimes numbering in their tens of thousands - are united by their loathing of ousted former premier Thaksin Shinawatra, Yingluck's older brother.
They are demanding the end of the "Thaksin regime" and want an unelected "people's council" to replace the government, in a country that has suffered years of political turmoil.
While their numbers have fallen sharply since an estimated crowd of up to 180,000 people joined an opposition rally on November 24, the protesters have increasingly sought out high profile targets.
Vowing a final push to achieve victory, opposition protesters used piles of sandbags to try to climb over barriers protecting Government House.
"About 2,000 protesters of students network were trying to pressure the police" said National Police spokesman Piya Utayo, adding that demonstrators were believed to be bringing more sandbags to key locations.
"We have information that there will be efforts to escalate violence in several areas," he added.
Yingluck was not believed to be at Government House at the time.
At the same time a mob of opposition demonstrators also attacked a bus carrying "Red Shirt" government supporters heading to their own rally at a sports stadium on the other side of Bangkok, throwing paving stones and other objects, according to an AFP photographer at the scene.
Piya said police closed a nearby road to try to prevent further confrontations between the protesters and Red Shirts, who have massed in their tens of thousands.
But demo organisers are urging people to turn out in strength this weekend in a final push before celebrations for revered King Bhumibol Adulyadej's birthday on December 5, which is traditionally marked in an atmosphere of calm and respect.
Thaksin, a former telecoms tycoon, was ousted in a military coup in 2006 and lives in self-imposed exile, but he is widely believed to be the real power behind the embattled government of his younger sister Yingluck.
Pro-Thaksin Red Shirts, who have gathered in a stadium in Bangkok for a week, began stepping up their demonstrations Saturday, with tens of thousands expected at the site, vowing to protect the government.
PM calls for calm
"I want to ask protesters not to confront each other in a way that may lead to violence," Yingluck told reporters at a briefing at police headquarters on Saturday.
Hundreds of opposition protesters occupied parts of Telephone Organisation of Thailand (TOT) offices near their base at a key government complex in the outskirts of Bangkok Saturday, holding a cheerful picnic in the grounds.
They also briefly gathered around Communications Authority of Thailand (CAT), another key state telecoms firm.
"My fight strategy is to march empty handed. I feel tomorrow we will win," protester Sanit Ounjai, a 45-year-old rubber farmer from southern Thailand, told AFP.
Thaksin is adored by many of the country's rural and urban working class but hated by many southerners, middle-class Thais and the Bangkok elite, who see him as corrupt and a threat to the monarchy.
He remains a hugely divisive figure seven years after he was deposed by royalist generals.
Pro-Thaksin parties have won every election for more than a decade but Yingluck has given no indication that she is thinking of calling fresh polls as a way out of the crisis.
Demonstrators on Friday forced open the gates of the compound of the army headquarters in Bangkok and occupied the lawn inside for several hours, calling on the military to support their fight to bring down the government.
It was the latest in a string of provocative moves targeting a symbol of state power, which have made headlines but failed to rattle the government into acting to disperse their rallies.
Yingluck on Saturday said security officials were "ready to defend" Government House, but added that they would do so with "leniency".
Yingluck's Puea Thai party came to power in 2011 elections on a wave of Thaksin support, after a bloody 2010 military crackdown on Red Shirt protests under the previous government left some 90 people dead.
The protests began on October 30 in response to a ruling party amnesty plan that could have allowed Thaksin's return, and have snowballed despite the Senate's rejection of the bill.