About 100,000 anti-government protesters gathered in Thailand's capital yesterday, as tensions between Bangkok's middle classes and the mostly rural supporters of ousted Prime Minister Thaksin Shinawatra threatened to boil over.

The protests led by the opposition Democrat Party mark the biggest demonstrations since deadly political unrest in April-May 2010, when Mr Thaksin's red-shirted supporters paralysed Bangkok to try to remove a Democrat-led government.

Thaksin's sister, Yingluck Shinawatra, is now in power after winning a 2011 election that was seen as a victory for the working poor and a defeat for the traditional Bangkok elite that includes top generals, royal advisers, middle-class bureaucrats, business leaders and old-money families.

After a delicate calm for the past two years, fissures between those two rival political forces are opening.

About nine miles away in a stadium about 40,000 pro-government "red shirts" rallied in support of the prime minister. Many came by bus from rural provinces in the north and northeast.

Ms Yingluck has been pilloried by her critics as a puppet for her brother, who was ousted in a 2006 military coup and convicted two years later of graft, which he has denied. He has lived in self-imposed exile since 2008.

"We have stood by silently while her brother calls the shots and she runs the country into the ground with loss-making policies," said Suwang Ruangchai, 54, who is from Surat Thani in the south.