* Police ask military to help with security
* Crowd attacks people close to pro-government stadium rally
* Judicial intervention unlikely - minister
Gunshots were fired and an anti-government crowd attacked motorcyclists and vehicles near a stadium rally by supporters of Thai Prime Minister Yingluck Shinawatra on Saturday, as tensions boiled over amid attempts to topple her from power.
Several people were wounded when shots were fired as chaos erupted in Bangkok's Ramkamhaeng area, where protesters armed with sticks attacked a bus and taxi and badly beat two people, police and Reuters witnesses said.
The U.S. embassy in Bangkok expressed concern about the rising political tension. It was unclear who had fired the shots and how many people were injured, Adul Saengsingkaew, national police commissioner-general, told Reuters.
With a Sunday deadline set by demonstrators for the ousting of the government, police called for military backup to protect parliament and Yingluck's office, Government House, where protesters tore down stone and razor wire barriers ahead of a planned move to occupy it.
Demonstrators have started to up the ante and briefly occupied the headquarters of the army on Friday, urging it to join them in a complex power struggle centred on the enduring political influence of Yingluck's billionaire brother, ousted prime minister Thaksin Shinawatra.
Those attacked by the crowd were accused of being "red shirts", ardently loyal supporters of Yingluck and Thaksin, who gathered in their thousands at the Rajamangala stadium to ward of any coup attempt against the government.
The tension heightens a nearly decade-long conflict that broadly pits Thailand's traditional establishment of top generals, royalists and the urban middle class against the mostly rural, northern supporters of Thaksin.
Protest leader Suthep Thaugsuban told supporters late on Friday to surround the headquarters of the national and city police, along with Government House and even a zoo on Sunday.
"We need to break the law a little bit to achieve our goals," said Suthep, a deputy prime minister in the previous government, routed by Yingluck in a 2011 election.
Thaksin remains intensely polarising. He was removed in a 2006 military coup and convicted two years later of graft, on charges he calls politically motivated. He is closely entwined with the government from self-imposed exile, sometimes meeting with Yingluck's cabinet by webcam.
Yingluck's son was harassed by parents of other children at his school on Friday, according to Thai media. In an emotional plea, she urged them to leave her son alone.
"I beg, if you have children you'll understand the heart of a mother," she said during a televised news conference. "If you're angry, please make it all about me."
A crowd of about 2,000 people massed outside state-owned telecoms companies on Saturday and Suthep has urged his followers to move on the ministries of labour, foreign affairs, education and interior. It remains unclear whether he has the numbers to besiege multiple government offices.
National Security Chief Paradorn Pattanathabutr told Reuters Government House or the police headquarters would not be seized. Late on Saturday, an army spokesman said navy, air force and army personnel had been called in as backup guards.
Suthep has called for a "people's council", which would select "good people" to lead the country, effectively suspending Thailand's democratic system. Yingluck has rejected that step as unconstitutional and has repeatedly ruled out a snap election.
The protesters have accused the government of acting unlawfully, after senior members of the ruling Puea Thai Party refused to accept a Nov. 20 Constitutional Court ruling that rejected their proposal for a fully elected Senate, which would have boosted the party's electoral clout. Puea Thai says the judiciary has no right to intervene in the legislative branch.
The ruling casts a spotlight on Thailand's politicised courts, which annulled an election won by Thaksin in 2006 on a technicality and later dissolved his Thai Rak Thai Party for electoral fraud. Its next incarnation, the People's Power Party, suffered the same fate. Nearly 150 executives of both parties were banned for five years.
Democrat leader Abhisit Vejjajiva, a former prime minister, said Yingluck had "acted above the law" by rejecting the Constitutional Court ruling.
Chaturon Chaisang, education minister and a close ally of Thaksin, said those accusations lacked rationale.
"The government, the prime minister and the cabinet have said nothing about accepting or not accepting the Constitutional Court decision," Chaturon told Reuters, adding that any attempts to use the courts to try to topple the government were unlikely to succeed this time.
The protests are the biggest since red-shirted Thaksin supporters paralysed Bangkok in April-May 2010 in a period of unrest that ended with a military crackdown in which 91 people, mostly Thaksin supporters, were killed.
Friday's peaceful invasion of the army headquarters illustrates how the protesters see the military as a potential ally because of its attempts to intervene against governments led or backed by Thaksin over the last decade.
Army chief Prayuth Chan-ocha, however, told protesters not to drag the military into politics.