About 100,000 anti-government protesters gathered in Thailand’s capital yesterday, as simmering 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 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 once again.

The rally was their biggest turnout yet. About 15 kilometres away, in a stadium at the opposite end of the city, about 40,000 pro-government “red shirts” rallied in a show of support of the Prime Minister. Many came by bus from rural provinces in the north and northeast.

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, but exerts enormous influence on the policies of his sister’s government.

“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.

Biggest demonstrations since 2010 political violence

Few people in modern Thai history have been as polarising as Thaksin, a billionaire former telecommunications tycoon rev-ered by the poor and reviled by the elite.

In 2001, he became the first leader in Thai history to win a Parliamentary majority, and formed the first elected government to serve a full term, after which it was re-elected.